Power tool safety mechanisms

ABSTRACT

A sensing mechanism ( 12 ) for detecting user contact with an active portion ( 26 ) of the power tool ( 10 ) is provided. In addition, a safety mechanism ( 14 ) for preventing prolonged user contact with the active portion ( 26 ) of a power tool ( 10 ) is provided. The safety mechanism ( 14 ) is configured to actuate upon receipt of a signal from the sensing mechanism ( 12 ). According to a first aspect, the safety mechanism ( 14 ) is arranged to rapidly displace the active portion ( 26 ) away from a user extremity. Alternatively, according to a second aspect, the safety mechanism ( 14 ) is arranged to rapidly urge an extremity of the user away from the active portion ( 26 ) of the power tool ( 10 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of International ApplicationNo. PCT/US02/21790, filed Jul. 11, 2002. This application claims thebenefit of U.S. Provisional Application No. 60/304,614, filed Jul. 11,2001, U.S. Provisional Application No. 60/309,352, filed Aug. 1, 2001,U.S. Provisional Application No. 60/323,511, filed Sep. 19, 2001, U.S.Provisional Application No. 60/340,191, filed Dec. 14, 2001, and U.S.Provisional Application No. 60/340,612, filed Dec. 14, 2001. Thedisclosure(s) of the above application(s) is (are) incorporated hereinby reference.

FIELD OF INVENTION

[0002] The present invention relates generally to a safety system for apower tool and, more particularly to various improved safety systems fora woodworking power tool that prevents or reduces potentially injuriouscontact between an active portion of the power tool and a portion of theoperators body.

BACKGROUND OF THE INVENTION

[0003] The advent of modern power tools has allowed many materialremoval and material forming processes that were typically performed byhand to be performed with greater efficiency, greater precision andtypically at a lower cost. The modern power tool is typically comprisedof three main systems, the power system, the tool system and a safetysystem. The power system transfers a first energy type to a secondenergy type that the tool system is able to use. The tool systemperforms the material removal or material forming processes using theenergy from the power system. Lastly, the safety system preventsdangerous conditions between the tool system and the operator of thepower tool.

[0004] Many devices utilize power systems to convert an energy sourceinto a useable form. In modern power tools, the power systems typicallyconvert either hydrocarbon based fuels or electrical energy intomechanical energy. Hydrocarbon fuel power systems are normally on suchdevices as chain saws and trimmers; whereas electrical power systems arefound on such devices as drills and table saws.

[0005] In many instances, the tool system of a power tool resembles thehand tool that was originally utilized to perform wood workingoperations. For example, a hand drill and a power drill both utilize adrill bit to remove material in a circular shape from a workpiece. Inother instances, modern power tools utilize tool systems that areunique. For example, a circular saw utilizes a circular shaped saw bladehaving a plurality of teeth disposed around the circumference of theblade. While the teeth of the circular saw blade are similar to the onesformed on a hand saw, the circular configuration on the bladefacilitates rotational motion of the blade as it engages a workpiece.

[0006] Since many of the safety systems set forth herein are describedin relation to either a table saw or a miter saw, each of these powertools are further described below. A typical table saw generallyincludes a base that supports a generally flat table top having alongitudinally extending throat slot or opening through which a sawblade or other cutting tool protrudes above the table for engaging aworkpiece. A motor is mounted beneath the table top, and the cuttingtool, typically a circular saw blade, is mounted for rotation to theoutput shaft of the motor. The saw blade is positioned to effect cuttingof the workpiece as it is moved longitudinally along the table. The sawblade can be lowered or raised with respect to the table top toaccommodate workpieces of varying thicknesses as well as adjusted tovarious angular orientations relative to the plane of the table top inorder to cut bevels or other such angular cuts on the workpiece.

[0007] Additionally, a typical miter saw generally includes a basemember having a slot formed therethrough for receiving a saw blade and apivotal support arm coupled to the base member. A saw is mounted to thedistal end of the support arm. When the arm is lowered, the saw bladeengages the workpiece, thereby cutting the workpiece. Additionally, themiter saw may include a mechanism for rotating the support arm around az-axis (upward) relative to the base member for performing angledcutting operations.

[0008] Various safety systems have been developed to minimize the riskof injury during the operation of such power tools. Exemplary power toolsafety systems may include guard mechanisms and operator detectionsystems. A guard physically prevents the operator from making physicalcontact with the active portions of the tool, such as belts, shafts,blades, etc. However, some power tools preclude the use of a guard thatwould effectively prevent the operator from making contact with theactive portion of the tool. In these instances, operator detectionsystems have been developed to prevent and/or reduce injurious contactbetween the operator and the active portion of the power tool.

[0009] A conventional operator detection system for a power tool isgenerally comprised of three primary subsystems: a detection subsystem,a control subsystem and a reaction subsystem. The detection subsystem orsensing mechanism tracks the proximity of the operator in relation tothe active portion of the power tool. The control subsystem determinesthe appropriate response to input received from the detection subsystem.Lastly, the reaction system or safety mechanism may initiate aprotective operation, if applicable, that prevents and/or reducespotentially injurious contact between the operator and the activeportion of the power tool. Each of these subsystems are furtherdescribed below.

[0010] Detection subsystems operatively determine the location of theoperator's body to the active portion of the power tool. Three knowntypes of detection means are currently employed. First, fixed detectionsubsystems utilize various sensing techniques to determine if aparticular portion of an operator's body is located in a certainposition proximate to the power. For example, a trigger mechanism may belocated on the handle portion of a miter saw. The trigger mechanismensures that the power tool is only operated when the operator's hand isgrasping the handle. If the operator's hand does not engage the triggermechanism, the power tool will not operate, thereby preventing injury tothe operator of power tool. If the trigger is disengaged when the powertool is operating, the trigger mechanism may cut power to the activeportion of the tool.

[0011] Second, proximate detection subsystems utilize various sensingtechniques to determine the proximity of the operator to the activeportion of the power tool. In one known approach, an electrical signalis transmitted through the active portion of the power tool. A receiveris coupled to the operator's body to receive the signal. When the activeportion of the power tool is brought in close proximity to the receiver,the received signal is increased. As the intensity of the receivedsignal increases, the control system determines if the signal intensityexceeds some predetermined threshold level. If so, the control subsystemmay initiate some protective operation to prevent and/or reduce operatorinjury.

[0012] Third, contact detection subsystems generally employ variouscapacitive sensing techniques to determine when the operator physicallytouches the active portion of the power tool. In one known approach, anelectrical signal is transmitted from a transmitter to a receiver, wherethe transmitter is capacitively coupled via the active portion of thetool to the receiver. When the operator touches the active portion,there is a sudden decrease in the signal level detected at the receiver.Accordingly, if the sensed signal level drops below some predeterminedthreshold level, the control subsystem may initiate some protectiveoperation to prevent and/or reduce operator injury.

[0013] Control subsystems determine an appropriate response to inputreceived from the detection subsystem. When the control systemdetermines that the operator's body is in dangerous proximity to theactive portion of the power tool, it may initiate some protectiveoperation to prevent and/or reduce operator injury.

[0014] The control subsystem may then interact, if applicable, with thereaction subsystem to carry out a protective operation that preventsand/or reduces potentially injurious contact between the operator andthe active portion of the power tool. The reaction system may preventand/or reduce the potential of operator injury in one of a variety ofways. For example, a braking mechanism may be employed to slow or stopmovement of the active portion of the tool. Alternatively, an activeretraction mechanisms may operatively moves the active portion of thetool away from of the operator's body, thereby prevent injuriouscontact.

[0015] The present application sets forth numerous improved safetymechanisms for preventing and/or reducing potentially injurious contactbetween an operator and active portion of a power tool. At least oneknown safety system for power tools is set forth in InternationalPublication No. WO 01/26064 which is incorporated by reference herein.It is to be understood that the safety mechanisms set forth below may beintegrated with this exemplary safety system and/or other known powertool safety systems. For a more complete understanding of the presentinvention, its objects and advantages, reference may be had to thefollowing specification and to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a block diagram of the sensing mechanism and safetymechanism configuration of the present invention;

[0017]FIG. 2 is view of a sensing mechanism according to a firstembodiment of the present invention;

[0018]FIG. 3 is a perspective view of a sensing mechanism employed in anexemplary miter saw according to a second embodiment of the presentinvention;

[0019]FIG. 4 is a front view of the sensing mechanism of FIG. 3 shownaccording to an alternative embodiment;

[0020]FIG. 5 is a perspective view of a sensing mechanism employed in anexemplary miter saw according to a third embodiment of the presentinvention;

[0021]FIG. 6 is a diagram of an exemplary table saw which may employ asensing mechanism according to a fourth embodiment of the presentinvention;

[0022]FIG. 7 is a block diagram of a preferred embodiment of the sensingmechanism of FIG. 6;

[0023]FIG. 8 is a graph illustrating a parasitic load making contactwith a blade of the table saw of FIG. 6;

[0024]FIG. 9 is a graph illustrating three exemplary impedance loadingconditions on the blade of the table saw of FIG. 6;

[0025]FIG. 10 is a graph illustrating the three exemplary impedanceloading conditions according to FIG. 9 having added constant parasiticload;

[0026]FIG. 11 is a graph illustrating the detected signal level inrelation to varying parasitic loads which may be associated with theoperation of the table saw of FIG. 6;

[0027]FIG. 12 is a graph illustrating the detected signal level of FIG.11 including an ideal curve and the basis for the adjustable thresholdvalue;

[0028]FIG. 13 is a graph of the drive voltage of the transmitter inrelation to the voltage detected at the receiver for each of theoperating conditions of FIG. 12;

[0029]FIG. 14 is a schematic of an exemplary circuit used to derive adynamically adjustable threshold value in accordance with the presentinvention;

[0030]FIG. 15 illustrates a known capacitive sensing system;

[0031]FIG. 16 illustrates a block diagram of a sensing mechanismaccording to a fifth embodiment of the present invention;

[0032]FIG. 17 is a signal representation of the sensing mechanism ofFIG. 16 having a signal amplitude near zero;

[0033]FIG. 18 is a signal representation of the sensing mechanism ofFIG. 17 shown with an operator's hand touching a handle of the powertool;

[0034]FIG. 19 is a graph of an exemplary sinusoidal voltage employed toreduce the amount of EMI radiation emitted from the capacitive sensingsystem of FIG. 16;

[0035]FIG. 20 is a perspective view of a sensing mechanism according toa sixth embodiment of the present invention;

[0036]FIG. 21 is a cutaway view of a sensing mechanism according to aseventh embodiment of the present invention;

[0037]FIG. 22 is a cutaway view of a sensing mechanism according to aeighth embodiment of the present invention;

[0038]FIG. 23 is a perspective view of a sensing mechanism according toa ninth embodiment of the present invention;

[0039]FIG. 23b is a perspective view of a sensing mechanism according toa seventh embodiment of the present invention;

[0040]FIG. 24 is a side view of a safety mechanism according to a firstembodiment of the present invention;

[0041]FIG. 25 is a side view of a safety mechanism according to a secondembodiment of the present invention;

[0042]FIG. 26a is a side view of a safety mechanism according to a thirdembodiment of the present invention shown prior to actuation;

[0043]FIG. 26b is a side view of the safety mechanism of FIG. 26a shownafter actuation;

[0044]FIG. 27 is a perspective view of a safety mechanism according to afourth embodiment of the present invention;

[0045]FIG. 28 is a cutaway view of the safety mechanism of FIG. 27 shownprior to actuation;

[0046]FIG. 29 is a cutaway view of the safety mechanism of FIG. 27 shownsubsequent to actuation;

[0047]FIG. 30 is a side view of a safety mechanism according to a fifthembodiment of the present invention shown prior to actuation;

[0048]FIG. 31 is a side view of a safety mechanism of FIG. 30 shownsubsequent to actuation;

[0049]FIG. 32 is a cutaway view of the safety mechanism of FIG. 30 takenalong line 32-32 of FIG. 30.

[0050]FIG. 33 is a side view of a safety mechanism according to a sixthembodiment of the present invention prior to activation;

[0051]FIG. 34 is a side view of the safety mechanism of FIG. 33 shownsubsequent to activation;

[0052]FIG. 35 is a side view of a safety mechanism according to aseventh embodiment of the present invention shown prior to activation;

[0053]FIG. 36 is a side view of the safety mechanism of FIG. 35 shownsubsequent to activation;

[0054]FIG. 37 is a side view of a safety mechanism according to a eighthembodiment of the present invention shown prior to activation;

[0055]FIG. 38 is a side view of the safety mechanism of FIG. 37 shownsubsequent to activation;

[0056]FIG. 39a is a side view of a safety mechanism according to a ninthembodiment of the present invention shown immediately after activation;

[0057]FIG. 39b is a side view of the safety mechanism of FIG. 39a shownafter engagement with a user;

[0058]FIG. 40a is a side view of a safety mechanism according to a tenthembodiment of the present invention shown prior to activation;

[0059]FIG. 40b is a side view of the safety mechanism of FIG. 40a shownafter activation;

[0060]FIG. 41 is a side view of a safety mechanism according to aeleventh embodiment of the present invention shown prior to activation;

[0061]FIG. 42 is a side view of the safety mechanism of FIG. 41 shownafter activation;

[0062]FIG. 43 is a side view of a safety mechanism according to atwelfth embodiment of the present invention shown prior to activation;

[0063]FIG. 44 is a side view of the safety mechanism of FIG. 43 shownafter activation;

[0064]FIG. 45 is a side view of a safety mechanism according to athirteenth embodiment of the present invention shown prior toactivation;

[0065]FIG. 46 is a side view of the safety mechanism of FIG. 45 shownafter activation;

[0066]FIG. 47a is a side view of a safety mechanism according to afourteenth embodiment of the present invention shown prior toactivation;

[0067]FIG. 47b is a side view of the safety mechanism of FIG. 47a shownafter activation;

[0068]FIG. 47c is a side view of a safety mechanism according to afifteenth embodiment of the present invention shown prior to activation;

[0069]FIG. 47d is a perspective view of the leaf spring stop of thesafety mechanism of FIG. 47c;

[0070]FIG. 48 is a perspective view of a safety mechanism according to asixteenth embodiment of the present invention;

[0071]FIG. 49 is a cutaway view of the safety mechanism of FIG. 48 shownprior to actuation;

[0072]FIG. 50 is a cutaway view of the safety mechanism of FIG. 48 shownsubsequent to actuation;

[0073]FIG. 51 is a side view of a safety mechanism according to aseventeenth embodiment of the present invention shown prior toactivation;

[0074]FIG. 52 is a side view of the safety mechanism of FIG. 51 shownafter activation;

[0075]FIG. 53 is a side view of a safety mechanism according to aeighteenth embodiment of the present invention shown prior toactivation;

[0076]FIG. 54 is a side view of the safety mechanism of FIG. 53 shownafter activation;

[0077]FIG. 55 is a side view of a safety mechanism according to anineteenth embodiment of the present invention shown prior toactivation;

[0078]FIG. 56 is a side view of a safety mechanism according to atwentieth embodiment of the present invention shown prior to activation;

[0079]FIG. 57 is a perspective view of a safety mechanism according to atwenty-first embodiment of the present invention;

[0080]FIG. 58 is a side view of the safety mechanism of FIG. 57 shownprior to activation;

[0081]FIG. 59a is a side view of a safety mechanism according to atwenty-second embodiment of the present invention shown prior toactivation;

[0082]FIG. 59b is a side view of the safety mechanism of FIG. 59a shownafter activation;

[0083]FIG. 60a is a side view of a safety mechanism according to atwenty-third embodiment of the present invention shown prior toactivation;

[0084]FIG. 60b is a side view of the safety mechanism of FIG. 60a shownafter activation;

[0085]FIG. 61a is a side view of a safety mechanism according to atwenty-forth embodiment of the present invention shown prior toactivation;

[0086]FIG. 61b is a side view of the safety mechanism of FIG. 61a shownafter activation;

[0087]FIG. 62a is a side view of a safety mechanism according to atwenty-fifth embodiment of the present invention shown prior toactivation;

[0088]FIG. 62b is a side view of the safety mechanism of FIG. 62a shownafter activation;

[0089]FIG. 63a is a view of a safety mechanism according to atwenty-sixth embodiment of the present invention;

[0090]FIG. 63b is a side view of the friction stopping device of FIG.63a;

[0091]FIG. 63c is a view of a safety mechanism according to atwenty-seventh embodiment of the present invention;

[0092]FIG. 64a is a side view of a safety mechanism according to atwenty-eighth embodiment of the present invention shown prior toactivation;

[0093]FIG. 64b is a side view of the safety mechanism of FIG. 64a shownafter activation;

[0094]FIG. 64c is a side view of a safety mechanism according to atwenty-ninth embodiment of the present invention shown prior toactivation;

[0095]FIG. 64d is a side view of the safety mechanism of FIG. 64c shownafter activation;

[0096]FIG. 64e is a side view of a safety mechanism according to athirtieth embodiment of the present invention shown prior to activation;

[0097]FIG. 64f is a side view of the safety mechanism of FIG. 64e shownafter activation;

[0098]FIG. 64g is a side view of a safety mechanism according to athirty-first embodiment of the present invention shown prior toactivation;

[0099]FIG. 64h is a side view of the safety mechanism of FIG. 64g shownafter activation;

[0100]FIG. 64i is a side view of a safety mechanism according to athirty-second embodiment of the present invention shown prior toactivation;

[0101]FIG. 64j is a side view of the safety mechanism of FIG. 64i shownafter activation;

[0102]FIG. 65a is a view of a safety mechanism according to athirty-third embodiment of the present invention;

[0103]FIG. 65b is a view of the safety mechanism of FIG. 65a shownremoved from the exemplary miter saw;

[0104]FIG. 66a is a view of a safety mechanism according to athirty-fourth embodiment of the present invention;

[0105]FIG. 66b is a sectional view of the safety mechanism of FIG. 66ataken about line 66 b-66 b of FIG. 66a shown prior to activation;

[0106]FIG. 66c is a sectional view of the safety mechanism of FIG. 66bshown after activation;

[0107]FIG. 67a is a top view of a safety mechanism according to athirty-fifth embodiment of the present invention;

[0108]FIG. 67b is a side view of the safety mechanism of FIG. 67a;

[0109]FIG. 68a is a side view of a safety mechanism according to athirty-sixth embodiment of the present invention shown prior toactivation;

[0110]FIG. 68b is a side view of the safety mechanism of FIG. 68a shownafter activation;

[0111]FIG. 69 is a side view of a safety mechanism according to athirty-seventh embodiment of the present invention;

[0112]FIG. 70 is a side view of a safety mechanism according to athirty-eighth embodiment of the present invention;

[0113]FIG. 71 is a sectional view of a protection mechanism according toa first embodiment of the present invention;

[0114]FIG. 72 is a sectional view of a protection mechanism according toa second embodiment of the present invention;

[0115]FIG. 73 is a sectional view of a protection mechanism according toa third embodiment of the present invention;

[0116]FIG. 74a is a side view of a safety mechanism according to athirty-ninth embodiment of the present invention shown prior toactivation;

[0117]FIG. 74b is a side view of the safety mechanism of FIG. 74a shownafter activation;

[0118]FIG. 75a is a side view of a safety mechanism according to afortieth embodiment of the present invention shown prior to activation;

[0119]FIG. 75b is a side view of the safety mechanism of FIG. 75a shownafter activation;

[0120]FIG. 76a is a side view of a safety mechanism according to aforty-first embodiment of the present invention shown prior toactivation;

[0121]FIG. 76b is a side view of the safety mechanism of FIG. 76a shownafter activation;

[0122]FIG. 77a is a side view of a safety mechanism according to aforty-second embodiment of the present invention shown prior toactivation;

[0123]FIG. 77b is a side view of the safety mechanism of FIG. 77a shownafter activation;

[0124]FIG. 78a is a perspective view of a safety mechanism according toa forty-third embodiment of the present invention;

[0125]FIG. 78b is a side view of the safety mechanism of FIG. 78a shownadjusted to accommodate a small saw blade;

[0126]FIG. 78c is a side view of the safety mechanism of FIG. 78a shownadjusted to accommodate a large saw blade;

[0127]FIG. 79 is a perspective view of a safety mechanism according to aforty-fourth embodiment of the present invention;

[0128]FIG. 80 is a perspective view of a safety mechanism according to aforty-fifth embodiment of the present invention;

[0129]FIG. 81 is a perspective view of a safety mechanism according to aforty-sixth embodiment of the present invention;

[0130]FIG. 82 is a perspective view of a safety mechanism according to aforty-seventh embodiment of the present invention;

[0131]FIG. 83 is a perspective view of a safety mechanism according to aforty-eighth embodiment of the present invention;

[0132]FIG. 84 is a perspective view of a safety mechanism according to aforty-ninth embodiment of the present invention;

[0133]FIG. 85 is a perspective view of a safety mechanism according to afiftieth embodiment of the present invention;

[0134]FIG. 86 is a perspective view of a safety mechanism according to afifty-first embodiment of the present invention;

[0135]FIG. 87 is a perspective view of a safety mechanism according to afifty-second embodiment of the present invention;

[0136]FIG. 88 is a perspective view of a safety mechanism of FIG. 87employing a bumper stop;

[0137]FIG. 89 is a perspective view of a safety mechanism according to afifty-third embodiment of the present invention;

[0138]FIG. 90 is a perspective view of a safety mechanism according to afifty-third embodiment of the present invention;

[0139]FIG. 91 is a side view of a safety mechanism according to afifty-fourth embodiment of the present invention;

[0140]FIG. 92 is a side view of the braking system of the safetymechanism of FIG. 91;

[0141]FIG. 93 is a partial top view of a braking system constructed inaccordance to a second embodiment of FIG. 91;

[0142]FIG. 94 is a partial top view of a braking system constructed inaccordance to a third embodiment of FIG. 91;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0143] With reference to FIG. 1, the plurality of safety systems 20 setforth in the following embodiments generally include three mainsubsystems, namely a power tool 10, sensing mechanism 12 and safetymechanism 14. Each subsystem disclosed herein includes a variety ofconfigurations employing several components for each subsystem. As willbe further described below, these subsystems may be used in conjunctionor in various combinations to achieve specific safety advantages. Forclarity, each power tool 10, sensing mechanism 12 and safety mechanism14 described herein will include a unique suffix such as a, b, c etc.

[0144] It will be understood that the various safety mechanisms 14 setforth herein may be integrated with this or other well known power toolsafety systems. Moreover, while a preferred embodiment of a safetymechanism 14 may be shown in conjunction with a particular power tool10, it is envisioned that the various safety mechanisms may be adaptedfor use with other types of power tools.

[0145] Safety Guard Switch

[0146] As shown generally in FIG. 2, power tool 10 a includes a mitersaw having a circumferential guard 18. Although the followingdescription is directed to a miter saw, it will be appreciated that thesafety device described herein may also be used in conjunction withother power tools employing a safety guard. Miter saw 10 a has acircular saw blade 26 which is shielded by the guard 18. The guard 18 ispivotally attached to miter saw 10 a, and also has a pivot arm assembly28 linked between the miter saw arm 32 and the guard 18 to help ensureproper articulation of the guard 18 throughout the range of movement ofthe miter saw 10 a. Prior to or during a cutting procedure on workpiece30, it may be necessary for the operator to change the saw blade 26. Togain sufficient access to the saw blade 26, the user typically removesthe safety guard 18.

[0147] According to a preferred embodiment, sensing mechanism 12 aincludes a switch or sensing device 22 disposed on the safety guard 18to detect the position of the guard 18. When the guard 18 is notinstalled, or installed improperly, the sensing device 22 precludesoperation of the electric motor (not specifically shown) therebydisabling blade 26. Likewise, if the guard 18 is positioned in theproper orientation, the switch 22 enables operation of the electricmotor and consequently rotation of saw blade 26. Switch 22 preferablyincludes a pair of electrical contacts, one positioned on guard 18 andone positioned on a guard mounting hub 24 disposed on pivot arm 32. Inthis regard, when guard 18 is properly mounted on hub 24, the electricalcontacts form a complete electrical loop allowing switch 22 to permitoperation of the electric motor. It will be appreciated that switch 22may comprise alternate sensing mechanisms which adequately identify aproper orientation of guard 18.

[0148] Dual Safety Switch System

[0149] With reference to FIG. 3 a power tool 10 b employing a sensingmechanism 12 b according to a second embodiment of the present inventionis shown. The exemplary power tool embodied herein is a miter saw,however it is appreciated that the safety system of the presentinvention may be adapted for use with a variety of power tools. Mitersaw 10 b generally comprises a base portion 40, an angularly movabletable assembly 42, and an angularly movable housing assembly 44 having apivotally attached drive assembly 46. The drive assembly 46 is generallycomprised of an electrical motor 48 drivingly coupled by way of anextension arm 50 to saw blade 52. Positioned at the distal end of thearm 50 is saw blade 52 and a handle portion 54 for controllingarticulation of the saw blade 52 to engage a workpiece. The base portion40 of the miter saw 10 b includes a fence portion 56 for positioning aworkpiece relative to the saw blade 52. The electrical motor 48 of thepower tool 10 b is activated by a trigger mechanism 58 located in thehandle portion 54 of the arm 50

[0150] In operation, an operator positions a workpiece along the fence56 of the base portion 40 and activates the trigger mechanism 58 tooperate the saw blade 52. During operation, the operator articulates thesaw blade 52 into engagement with the workpiece to remove a portion ofthe workpiece. According to the present invention, a sensing mechanism12 b operatively detects the location of the operator's first and secondhand during operation of the power tool 10 b to ensure that theoperator's first and second hands are away from the saw blade 52 of thepower tool 10 b to reduce the chance of injurious contact between aportion of the operator's body and the active portion of the power tool10 b.

[0151] The sensing mechanism 12 b generally includes a first switch orsensor 66 positioned in the handle portion 54 of the power tool 10 boperable to detect an operator's first hand, a second switch or sensor68 positioned in a second location operable to detect an operator'ssecond hand and a controller coupled to the first and second sensorsoperable to prevent operation of the power tool 10 b when either thefirst or the second sensors do not detect an operator's hand. Thesensing mechanism 12 b reduces/prevents potentially injurious situationsbetween the operator's hands and the active portion of the power tool 10b by ensuring that the operator's hands are located away from the sawblade 52 during operation of the power tool 10 b.

[0152] The first sensor 66 of the sensing mechanism 12 b is located inthe handle portion 54 of the power tool 10 b. The first sensor 66ensures that the operator's first hand is placed on the handle 54. Asshown in FIG. 3, the first sensor 66 is located along an upper portionof the handle 54. The first sensor is preferably oriented to allow theoperator to easily activate the first sensor 66 during normal operationof the power saw 10 b. It is appreciated that first sensor 66 may belocated at other locations on handle 54.

[0153] The second sensor 68 of the sensing mechanism 12 b is positionedto prevent injurious contact between the operator's second hand and theactive portion of the power tool 10 b. As shown in FIG. 3, the secondsensor 68 is located along the left side of the fence portion 68 of thepower tool 10 b. In this location, the second hand of the operator willbe positioned away from the active portion 60 of the power tool 10 b. Itis appreciated that the second sensor 68 may be located at variouspositions on the power tool 10 b to ensure that the second hand of theoperator is safely away from the saw blade 52 of the power tool 10 b.For example, in an alternate embodiment shown in FIG. 4, power tool 10b′ includes a second sensor 68′ located along the front of the baseportion 42 of the miter saw to ensure that the operator's second hand issafely away from the active portion of the power tool 10 b′. Thisconfiguration allows a user to depress sensor 68 with a thumb whilemanipulating the workpiece with fingers safely away from active portion60 of power tool 10 b′.

[0154] Returning to FIG. 3, it is contemplated that a plurality ofsecond sensor's may be used with the sensing mechanism 12 b of thepresent invention to allow for alternative configurations of theoperator's hands. For example, second sensors may be positioned alongthe left side and the right side of the fence 56. In this configurationa left or right handed operator could utilize the safety system of thepresent invention during operation of the power tool 10 b.

[0155] The controller (not specifically shown) is coupled to the firstand second sensors 66, 68 and the electric motor of the power tool 10 b.The controller is operable to allow operation of the power tool 10 bwhen the first and the second sensors 66, 68 detect the first and secondhands of the operator, respectively. If the controller detects that theoperator's hands are in the correct position, the saw blade 52 of thepower tool 10 b is allowed to be operated. The controller of the presentinvention may be any of a variety of controllers, microcomputers orother devices suitable to detect activation of the first and secondsensors 66, 68 and in turn allow operation of the saw blade 52.

[0156] The controller is preferably coupled to the first sensor 66 andthe second sensor 68 in a series type configuration. In the series typeconfiguration the controller includes a single input and single outputconnected to the controller. The first and second sensors 66, 68 areconnected to the single input and single output to form a loop. Thecontroller detects the desired positioning of the operator's hands whenthe first and the second sensors 66, 68 are both activated, allowing acompletion of the circuit from the input to the output. When thecontroller detects that the first and second hands of the operator arein the desired position, the controller allows operation of the powersaw 10 b.

[0157] The controller may also be coupled to the first and secondsensors 66, 68 in a parallel type configuration. In a parallelconfiguration, each of the first and the second sensors are coupled to aseparate input and a separate output on the controller. The parallelconfiguration requires that the controller determine that both the firstand the second sensors 66, 68 are activated at the same time to allowoperation of the saw blade 52 of the power tool 10 b.

[0158] In a preferred embodiment, the first sensor 66 is located in thehandle portion 54 of the miter saw 10 b and is activated while theoperator is grasping the handle portion 54 of the miter saw and thesecond sensor 68 is located along the fence 56 of the miter saw 10 b. Inoperation, the operator of the miter saw 10 b activates the first switch66 while grasping the handle portion 54 and activates the second switch68 while holding a workpiece against the fence portion 56. In thisconfiguration, both the operator's first and second hands are locatedaway from the saw blade 52 of the power tool 10 b. The first and secondsensors 66, 68 may be any of a variety of sensors that detect thepresence of an operator's hand. A preferred sensor is a electricalswitch sensor that is activated when a portion of the operator's handdepresses a plunger or other device to indicate physical presence of theoperator's hand.

[0159] Another type of sensor that may be used for the first and thesecond sensors are electromagnetic signal sensors. The electromagneticsignal sensor transmits an electrical signal from a transmitter. Areceiver, typically adjacent to the transmitter receives the transmittedelectromagnetic signal. The received electromagnetic signal is comparedto a threshold value to determine if the operator's hand is proximal tothe sensor. The electromagnetic signal sensor signals the controller tothe presence of the operator's hand. Some commonly known electromagneticsignal sensors are proximity switches, light curtains or hall effectsensors.

[0160] Yet another type of sensor that may be used for the first andsecond sensors 66, 68 are electrical capacitance sensors. Electricalcapacitance sensors are typically comprised of a capacitance measuringdevice that determines the electrical capacity around the sensor. Theelectrical capacitance sensor monitors the electrical capacity andcompares it to a threshold value. Generally, when a portion of theoperator's hand comes in close proximity or touches the sensor, theelectrical capacity increases. If the capacitance exceeds a thresholdvalue, the electrical capacitance sensor signals the controller to thepresence of the operator's hand.

[0161] During many operations, the operator will utilize one of his/herhands to guide the workpiece relative to the saw blade 60 or restrainthe workpiece relative to the saw blade 60. Therefore, it is desirableto locate the second switch 68 in a position that the operator normallyutilizes to guide or restrain the workpiece. In a first configuration,the operator's other hand is utilized to restrain a workpiece to theguide fence 56 of the power tool 10 b. The guide fence 56, as describedabove typically extends outward from a first and second side of the sawblade 52 to provide a guide that is relatively perpendicular to the sawblade 52. In this configuration, an operator may hold the workpiece tothe fence 56 by gripping the workpiece with their thumb and back of thefence with their fingers to clamp them together. In this configuration,a second switch 68 could be located along the rear of the fence 56 (asshown in FIG. 3, switch 68 is accessible from the front of fence 56 butmay alternatively be accessible at a location on the rear of fence 56)to allow the fingers of the operator to positively engage the secondswitch 68 when positioned away from the saw blade of the power tool.

[0162] Turning to FIG. 4, in a second configuration, a workpiece havinga relatively large width is restrained to the table portion 42 of thepower tool 10 b′ by an operator. In this configuration, the fingers ofthe operator are typically used to push downward on the workpiece torestrain it relative to the saw blade causing the thumbs of the operatortypically overhang the front edge of the table portion. In thisconfiguration, a switch is being mounted along the front edge of thetable portion of the miter saw. In this configuration, the operatorwould positively secure the second safety switch 68′ to indicate thathis first and second hands are not located within dangerous proximity ofthe saw blade 52 of the power tool 10 b′.

[0163]FIG. 5 shows a sensing mechanism 12 c in the form of a lightswitch that prevents a power tool 10C from being operated if a foreignobject is near the saw blade 52. Like reference numerals associated withmiter saw 10 c are used to denote like components identified in relationto miter saw 10 b. Sensing mechanism 12 c is composed of at least onelight emitting panel 70 and at least one light receiving panel 72 inoperative communication. Light emitting panel 70 is preferablypositioned at either the front or rear portion of the saw blade 52 andoriented to emit light along the planar direction of saw blade 52. Lightreceiving panel 72 is preferably positioned at the other of the front orrear portion of the saw blade and oriented to receive light emittedalong the planar portion of saw blade 52. If an object prevents lightfrom the light emitting panel 70 from being received by light receivingpanel 72, saw blade 52 is stopped to prevent contact of the blade 52with a foreign object, namely a human extremity.

[0164] Light emitting and light receiving panels 70, 72 are connected toa controller (not specifically shown) as well as electric motor 48. Whenlight is not received by light receiving panel 72, the controller shutsdown power to electric motor 48.

[0165] Capacitive Sensing

[0166] 1. Variable Limit Setting Based on Parasitic Load

[0167]FIG. 6 illustrates an exemplary table saw 10 d, which may employ asensing mechanism 12 d in accordance with the present invention. Thetable saw 10 d generally includes a table portion 102 having a slot 104therethrough for receiving a saw blade 106. The saw blade 106 is indriving engagement with a motor assembly (not shown) as is well known inthe art. To cut a workpiece, the operator 108 guides a workpiece 110into contact with the saw blade 106 as shown in FIG. 6. While thefollowing description is provided with reference to a table saw, it isreadily understood that the sensing mechanism 12 d of the presentinvention is applicable to a variety of power tools and/or woodworkingtools, including (but not limited to) miter saws, radial arm saws,circular saws, band saws, joiners, planers, nailers, drills, etc.

[0168] Sensing mechanism 12 d is configured to minimize and/or preventserious injury to the operator of the table saw 10 d as will be morefully described below. Briefly, the sensing mechanism 12 d is operableto detect the proximity of the operator 108 to the saw blade 106. Upondetection of a dangerous condition, the sensing mechanism 12 d willtrigger a protective operation intended to reduce the potential foroperator injury.

[0169]FIG. 7 illustrates the sensing mechanism 12 d of the presentinvention in the context of the above-described table saw 10 d. Thesensing mechanism 12 d is intended to determine if a human operator ofthe saw has made contact with an active portion of the saw 10 d. Theactive portion should be a conductive object that is inherentlydangerous, such as a saw blade, punch, press, router/drill bit or othermechanically moving device. In this case, the active portion of the sawis the saw blade 106.

[0170] To determine if the operator has touched the saw blade, an ACsignal coupled through the saw blade 106 is monitored for changes. To doso, the sensing mechanism 12 d includes a transmitter 112 capacitivelycoupled to the electrically isolated saw blade 106 (or arbor shaft)which in turn is capacitively coupled to a receiver 114. Morespecifically, the transmitter 112 is electrically coupled to atransmitting plate 118 disposed adjacent to the saw blade 106. Thetransmitting plate 118 is capacitively coupled to the saw blade 106,such that a charge on the transmitting plate 118 is mirrored to the sawblade 106. Likewise, a receiver plate 120 is capacitively coupled to thesaw blade 106 (or arbor shaft) in a similar manner as the transmitter112, so that this differential charge is also mirrored to the receiverplate 120. The receiver plate 120 is then electrically coupled to areceiver 114. In this way, the receiver 114 is configured to sense theAC signal from the transmitter 112.

[0171] When the human 108 touches the saw blade 106, it will cut intotheir skin. As the blade 106 touches the moist conductive tissue justbeneath the dry layer of skin cells, the electric charge on the blade106 will be shared with the human body 108. The sensed signal level atthe receiver 114 suddenly drops when the human operator comes intocontact with the saw blade 106. The human operator 108 is essentiallyshorting out the receiver 114. When there is such a rapid change in thedetected signal intensity, it is assumed that the operator 108 hastouched the saw blade 106.

[0172] Referring to FIG. 7, a detection circuit 126 is used to monitorthe signal intensity at the receiver 114. It is envisioned that thedetection circuit 126 may be constructed using well-known analog circuitcomponents or implemented in software embodied in a programmablecontroller. In any event, the detection circuit 126 is operable todetect a sudden drop in the signal intensity and, in response to suchsignal drop, to activate a protective operation such as a safetymechanism 14 disclosed herein which may prevent and/or reduce the riskof injury to the operator 108. For instance, the protective operationmay be a mechanical braking mechanism 130 that is actuated to stop therotation of the saw blade. It is to be understood that other protectiveoperations (e.g., visible or audible alarms) are also within the broaderaspects of the present invention.

[0173] Referring now to FIGS. 7 and 8, in order to maintain a measurablesignal at the receiver, feedback control may be utilized to control themagnitude of the signal level detected at the receiver 114. Since themagnitude of the sensed signal may be attenuated by various impedancefactors associated with the operation of the saw, the magnitude of thetransmitted signal (also referred to as the drive signal) is adjustedbased on the signal level detected at the receiver 114. Specifically,the detection circuit 126 continually monitors the magnitude of thesensed signal 134 in relation to a reference signal value 136. When themagnitude of the sensed signal 134 is above the reference value 32, themagnitude of the transmitted signal is reduced proportionally. On theother hand, when the magnitude of the sensed signal 134 is below thereference value 32, the magnitude of the transmitted signal isincreased. It is envisioned that feedback control is done at a lowfrequency so as not to interfere with the detection of operator contactwith the saw blade 106 As seen in FIG. 8, a sudden parasitic load makescontact with the blade 106 at time TO causing signal 134 to drop awayfrom calibration line 136. As FIG. 8 shows, increasing the transmittedoutput magnitude compensates for the drop in signal 134 and eventuallythe signal 134 will match the reference 138. Note that the signal 134did not cross the threshold 138 so the circuit never triggered a safetymechanism.

[0174] Referring to FIG. 9, a simulation shows three different impedanceloading conditions on the blade. In Stage 1, the signal 134 iscalibrated to the reference voltage 138. Neglecting feedback andapplying typical wet wood impedance to the blade would produce a drop inthe signal 134 as seen in Stage 2. The third stage of the simulation, isa result of only the human touching the blade without the parasiticload. For simplicity, the signal 134 is not compensated to display thedifferent attenuation levels between human and wood impedance loads. Inthis situation, the system will allow the impedance load in stage 2 butwill trigger in stage 3.

[0175]FIG. 10 represents the same simulation but with added constantparasitic load to all three stages. The system was initially allowed tocompensate for the new parasitic load (not shown before stage 1) as aresult, stage 1 is identical to FIG. 9. Stages 2 and 3, however, act inthe same manner as before but with different attenuation levels. In thiscase, none of the stages will trigger the safety mechanism. In thissituation, the threshold level 138 should have been increased above theStage 3 level but below the Stage 2 level.

[0176] Turning now to FIG. 11, to determine the best place for thethreshold level, the minimum impedance for stage 2 and the maximumimpedance for stage 3 are used across a wide range of nominal parasiticcapacitance. The minimum impedance is used for wood in stage 2 to keepthe curve 140 as low as possible (worst case.) The maximum humanimpedance is used in stage 3 to keep the curve 142 as high as possible(worst case.) Between these two curves is the ideal threshold level.FIG. 11 represents these curves plotted against the parasiticcapacitance. Clearly, a constant threshold voltage level would be proneto false trip and miss fire.

[0177] To illustrate this point, assume that the threshold voltage isset at 8.0 volts in FIG. 4. For stage 1 curve 144 & stage 2 curve 142,the sensing mechanism 12 d properly operates across a wide range ofparasitic capacitive loads. However, when capacitive loads associatedwith the saw exceed 400 pF, the sensing mechanism 12 d may not detectoperator contact with the saw blade 106. In other words, after humancontact, the voltage level for stage 3 curve 142 does not drop below the8.0-volt threshold. Conversely, if the threshold value is set at 8.3volts, the sensing mechanism 12 d would accurately detect operatorcontact with the saw blade 106 when capacitive loads exceed 400 pF, butmay inaccurately initiate protective measures when capacitive loads arebelow 75 pF. Accordingly, the threshold value for the sensing mechanism12 d should vary based on the parasitic capacitance associated with theoperation of the saw.

[0178]FIG. 12 illustrates the basis for an exemplary dynamicallyadjustable threshold value. The ideal curve 148, which is the basis forthe adjustable threshold value, is preferably plotted halfway betweenstage 2 curve 42 and stage 3 curve 40 in order maximize sensitivity ofthe detection system and yet minimize occurrence of false triggers.

[0179] Since the parasitic capacitance associated with the operation ofthe saw is not easily determined, it is envisioned that the adjustablethreshold value may be derived from another operational parameter of thesaw. For each of the operating conditions described above, FIG. 13 plotsthe drive voltage of the transmitter 112 in relation to the voltagedetected at the receiver 114. One skilled in the art will readilyrecognize that the curve for each different operating conditioncorrelates to the corresponding curves in FIGS. 8-12. In other words,the parasitic capacitance associated with the operation of the sawcorrelates to the drive voltage of the transmitter. Therefore, thedesired threshold value may also be correlated to the drive voltage ofthe transmitter 112.

[0180]FIG. 14 illustrates an exemplary analog circuit 150 that may beused to derive the adjustable threshold value in accordance with thedrive voltage of the present invention. While one exemplary embodimenthas been provided with specific components having specific values andarranged in a specific configuration, it will be appreciated that thisfunction may be constructed with many different configurations,components, and/or values as necessary or desired for a particularapplication. The above configurations, components and values arepresented only to describe one particular embodiment that has proveneffective and should be viewed as illustrating, rather than limiting,the present invention.

[0181] 2. Handle Mounted Transmitter/Receiver Pair for Proximity Sensing

[0182] Contrary to the first embodiment, the following is a descriptionof an alternate sensing mechanism 12 e hereinafter referred to asproximity sensing. Whereas the previous circuit triggered on the lack ofa signal, the following will trigger on the presence of a signal. FIG.15 illustrates a known capacitive sensing system 160. In system 160 atransmitter 162 is connected to the handle or trigger portion of thetool 164 and broadcasts a signal. The signal is capacitively coupled tothe operator 170. The receiver 172 is connected to the active portion ofthe tool 174. When the operator 170 is holding the tool correctly, thesignal is transmitted through the person 170 to the receiver 172. As theoperator 170 approaches the active portion of the tool 174, the signalintensity on the receiver 172 increases until some predetermined levelis reached. At that point a predetermined action is performed, such asbraking of motor/blade or other safety mechanism 14 disclosed herein toprevent and/or reduce bodily injury.

[0183] The improvement of the present invention, lies in the fact thatif the operator 170 is touching a grounded object (table surface 102 ofFIG. 6) the signal path is essentially shorted out. With the operator170 touching both the transmitter 162 and the grounded object, thesignal intensity in the operator 170 is very low. Even when accidentaloperator contact with the active portion of the tool 174 has occurred,the signal amplitude picked up by the receiver 172 might not be highenough to trigger an employed safety mechanism 14.

[0184] To correct this situation, a second receiver is needed. Referringto FIG. 16, sensing mechanism 12 e is shown. The addition of secondreceiver 180 and feedback control circuit 182 provide a constant signallevel in the operator 170 regardless of operator grounding. The receiver180 is mounted in relation to the transmitter 162 such that no couplingexists until the user 170 is grasping the handle or trigger portion ofthe tool. Only then, does the receiver 180 receive a signal. To thoseskilled in the art of antenna theory, it is easily recognized that thereceived signal amplitude will be proportional to the signal amplitudein the operator's body. FIG. 17 visually describes this system.Transmitter 200 and receiver 202 are located just inside the handle 204of the tool. A ground plane 206 is placed to cancel any signal thatwould naturally propagate from transmitter 200 to receiver 202. As shownby the electric field lines 208, the receiver signal amplitude is nearzero. In FIG. 18, the operator's hand 210 is wrapped around handle 204.The electric field lines picked up by the operator 170 are continuousaround the handle 204 because the human body is conductive. The fieldlines 206 now can reach the receiver 202 and provide signal amplitudeproportional to the amplitude in the operator 170.

[0185] The feedback control 182 regulates the transmitted signalamplitude. If the signal on the receiver 180 is greater than somepredetermined reference level, it is assumed that the level in theoperator 170 is greater than the desired amount as well. The feedbackcontrol 182 then decreases the amplitude of the transmitted signal untilthe signal strength on receiver 180 reaches the predetermined level. Incontrast, if the operator 170 holding the tool suddenly touches agrounded object, the signal strength in the operator 170 would drop.Accordingly, the signal on the receiver 180 would also drop. Thefeedback control 182 recognizes this and compensates by increasing thetransmitter amplitude. By keeping the signal in the operator 170constant, the signal received by the active portion of the tool 174 isproportional only to the distance from the operator 170 to the activeportion of the tool 174.

[0186] It is additionally possible to change the feedback control 182.Instead of modifying the transmitted amplitude, the feedback controlcould modify the threshold value. When the signal on the receiver 180 isdropping, the circuit would have the same sensitivity if the thresholdof original receiver 172 were lowered as well.

[0187] 3. Lowered EMI on Capacitive Sensing

[0188]FIG. 19 illustrates a method of reducing the amount ofelectromagnetic interference (EMI) radiation that is emitted from acapacitive sensing system. Outputting a sinusoidal voltage 184 on apiece of metal and detecting the received signal is the basis forcapacitive sensing. The greater the frequency and the greater theamplitude, the more sensitive the system is. Unfortunately, anyconductive object of changing voltage produces radiated EMI. Globalcompliance standards limit the amount of both conducted and radiatedfields from most electronic/electrical devices and machines. By varyingthe frequency of oscillation, there is not a single frequency radiated.Instead, there will be a band of frequencies with an elevated radiatedemission. Since the energy radiated will be the same in a singlefrequency versus a band of frequencies, the measured amplitude of theband will be much lower than the amplitude of the single frequency. Thelower the amplitude, the more likely the signal is below the requiredlimits.

[0189] Additionally, as is generally known any signal such as the ACsignal of the sensing mechanism 12 d when coupled to an electricallyconductive body such as a saw blade of the sensing mechanism 12 d, emitsradiated electromagnetic interference. The frequency of the radiatedelectromagnetic interference is directly related to the frequency of theAC signal that is transmitted to the active portion of the power tool.Also, the magnitude of the radiated electromagnetic interference isrelated to the magnitude AC signal that is transmitted to the activeportion of the power tool. Additionally, the capacitive sensing systemof the present invention generally increases in sensitivity as theamplitude and the frequency of the AC signal that is transmitted fromthe transmitter to the saw blade is increased. The electrical signalfield strength of radiated emissions in devices not intended to beradiation devices is limited by the Code of Federal Regulations for theprotection of operators and electromagnetic compatibility with otherelectronic devices. The Code of Federal Regulations 47 C.F.R. 15.109limits the amount of radiated emission based on the band of thefrequency of emission. Therefore, it is desirable to vary the frequencyof AC signal from the transmitter to allow a signal having large fieldstrength to be dispersed over multiple different emission bands. Thevariation of the frequency allows the relatively high amplitude of theAC signal to be dispersed over a broad band of frequencies to reduce thepeak radiated electromagnetic interference in a single frequency. Thebroad band of frequencies allows the capacitive sensing system of thepresent invention to operate at desired radiated EMI levels to conformto reduce interference with other electronic devices and provide saferoperation by the operator.

[0190] The frequency of the AC signal is preferably varied by a rampshaped function wherein the frequency is alternated between a minimumfrequency and a maximum frequency in a linear pattern. It is alsoappreciated that the frequency of the AC signal may be varied by otherpatterns such as sinusoidal, step, random or others to select anddisperse the level of the radiated EMI.

[0191] Alternative Sensing

[0192]FIG. 20 illustrates a safety system employing a sensing mechanism12 f according to an additional embodiment of the present invention. Thesensing mechanism 12 f detects when a portion of the operator's body isin dangerous proximity to the active portion of the power tool toprevent/reduce injuries. If a dangerous condition is detected, acontroller operates a protective measure such as a safety mechanism 14disclosed herein with respect to the active portion of the power tool.The sensing mechanisms 12 described according to this embodiment areshown operatively associated with a power table saw and a miter saw. Itwill be appreciated however, that the sensing system may also beemployed to other tools such as but not limited to planers, jointers ordrills.

[0193]FIG. 20 illustrates sensing mechanism 12 f including generator 202operatively associated with a miter saw 10 f, for detecting when a humanextremity is in close proximity to a rotating saw blade 204. Generator202 is an electrostatic charge generator attached to the rotating sawblade 204. If a human extremity or other object having a capacitance andcharge that is relatively lower than the charge on the saw blade 204, anelectrostatic charge in the form of a spark will act on the humanextremity. In a preferred embodiment, the generator 202 includes a VanDe Graff generator to generate the electrostatic charge however, it isappreciated that other electrostatic charge generators may be employed.The transfer of the spark to the operator's hand will alert the operatorthat a portion of his body is too close to the saw blade 204.

[0194]FIG. 21 shows a sensing mechanism 12 g including transmitter ordepth sensor 214 that senses if a human extremity is in close proximityto a rotating saw blade 208. Transmitter 214 is shown operativelyassociated with table saw 10 g and is operable to monitor the depth(thickness) of the workpiece 218 that is being fed into saw blade 208.In most cutting operations, the thickness of the workpiece 218 that isbeing cut is relatively consistent. In this way, if depth sensor 214detects a sudden change in the depth (thickness) of the workpiece 218, aswitch 216 is activated to stop saw blade 208 as a precautionary measureto prevent contact of human extremities with saw blade 208. It isappreciated that switch 216 may also comprise any of the safetymechanisms 14 disclosed herein.

[0195]FIG. 22 shows a sensing mechanism 12 h including light gate 226,which senses a change in the thickness of the workpiece 218 that sawblade 208 is cutting. Light gate 226 is shown in operative use with atable saw 10 h of the type explained above. Light gate 226 includes aplurality of light emitting diodes, (LEDs), 222 mounted to the undersideof table 224. Positioned above saw blade 208 for receiving the lightemitted from LEDs 222 are a plurality of photo-receivers 228.Photo-receivers 228 monitor the amount of light that is emitted fromLEDs 222. If the amount of light that is received by photo-receivers 228is less than a nominal amount or there is a significant change in theamount of light received, the saw blade 208 is shut off. Saw blade 208may be shut off by a switch or a safety mechanism 14 described herein.In operation, a human extremity or other object of thickness greaterthan the workpiece 218, positioned above the workpiece will affect theamount of light that is received by photo-receivers 228. In operation, asmall amount of light is emitted around the side and front of the blade208 because of the non-circular shape of the blade 208 and the enlargedwidth of the teeth with respect to the width of the blade 208. If anobject that is thicker than the workpiece 218 comes in close proximitywith the saw blade 208, a portion of the light that is emitted aroundthe side and front of the blade 208 is not received by thephoto-receivers 228.

[0196]FIG. 23a shows a sensing mechanism 12 i having an ultrasoundsensor panel 236, that senses if a human extremity, is in closeproximity to a rotating saw blade 208. As shown in FIG. 23a, the presentdevice is shown in operation with a table saw 10 i as described above.Ultrasound sensor 236 is generally comprised of a plurality ofultrasound emitters 230 and receivers 232 positioned therealong. Panel236 is positioned above the top of saw blade 208 so that panel 236including emitters 230 and receivers 232 extend beyond the point wheresaw blade 208 protrudes from planar top surface 224. In operation, aworkpiece 218 is moved toward a rotating saw blade 208 for selectiveremoval of a portion of the workpiece 218. As the workpiece 218 is movedtoward the saw blade 208, ultrasonic emitters 230 send out an ultrasonicsignal which is echoed off of the workpiece 218 and saw blade 208 andredirected toward receivers 232. Receivers 232, monitor the ultrasonicsignals to determine a profile, or height, of the workpiece 218 that isbeing cut. A change in the thickness, which may be caused by a humanextremity, changes the signal that is received by the receivers 232. Achange in the received signal activates a switch 240 which stops the sawblade 208 in order to prevent contact of the human extremity with thesaw blade 208. Again it is appreciated that any safety mechanism 14disclosed herein may be employed to stop saw blade 208 upon detectionfrom sensing mechanism 12 i.

[0197] Referring to FIG. 23b, a sensing mechanism 12 j includingproximity sensing guard 184 for a table saw 10 j is shown in detail. Atable saw assembly 10 j, as is well known is comprised of a table 186having a planar top surface 188. Formed in table 186 is an elongatedslot 190 for receiving a rotating circular saw blade 192 which isoperatively connected to a drive (not shown).

[0198] Proximity sensing guard 184 is operatively positioned above sawblade 192 to prevent accidental contact by the user with the saw blade192. Proximity sensing guard 184 is composed of a top plate 194 that ispositioned above saw blade 192 and substantially parallel planar topsurface 188. Connected to top plate 194 are a plurality of flexibleconductive sensing wires 196. In preferred operation, an electricalsignal transmitter (not shown) emits a predetermined signal to top plate194 and sensing wires 196. Attached to saw blade 192 is a receiver (notshown) which receives and monitors the signal that is emitted from topplate 194 and sensing wires 196. If an object with a relatively highcapacitance, like the human body comes in contact or close proximitywith sensing wires 196 or top plate 194, the amplitude of the signal isdramatically reduced. When the receiver receives a signal having arelatively low amplitude, indicating a high capacitance object is inclose proximity, a safety mechanism 14 is applied to the saw 10 j toprevent further rotation of the saw blade 192 leading to possiblecontact with a portion of the operator's body.

[0199] Moving Hands Away With Inertia

[0200] In many typical hand held portable circular saws, the blade isrotated in a clockwise direction as shown in FIG. 24. The direction ofrotation allows the saw blade to smoothly engage the workpiece withoutcausing the teeth of the saw blade to engage the workpiece and propelthe saw forward across the wood. Many commonly available handheldportable circular saws have a guard that prevents contact between theblade and other objects. However, the nature of a circular saw preventsthe guard from protecting the saw blade while the circular saw isoperating. Simply, the saw blade must be exposed to engage theworkpiece. Typically, the guards are rotated into engagement from therear of the saw to the front of the saw along a path that issubstantially similar to the perimeter of the blade. Many of the guardsare biased toward the closed position by a biasing mechanism.

[0201]FIG. 24 shows an exemplary miter saw 10 j which may employ asafety mechanism 14 j in accordance with the present invention. Safetymechanism 14 j limits the area of the blade 304 that is open to contact.Although the following description is directed to a miter saw 10 j, itwill be appreciated that the safety mechanism 14 j may also be used inconjunction with other tools employing a safety guard 308. Guard 308 ispivotally attached to miter saw 10 j and also includes a pivot armassembly 310 linked between miter saw arm 312 and guard 308 to helpensure proper articulation of guard 308 throughout the range of movementof miter saw 10 j.

[0202] Safety mechanism 14 j includes a trigger 306 that grasps the sideof saw blade 304, which is rotating clockwise, and causes the guard 308to close further around the blade 304 to prevent contact with the blade304. The trigger 306 is composed of a coupling mechanism 322 connectedto the guard that is operable to couple the guard 308 to the circularsaw blade 304. Once the coupling mechanism 322 has engaged the circularsaw blade 320, the guard 308 is actuated along direction 316 as shown inFIG. 24. As the guard 308 is actuated along direction 316, the guard 308engages any objects that are contacting the saw blade 304 or areproximate to the saw blade 304 thereby forming a barrier between the sawblade 304 and the operator.

[0203] Explained further, if an operator's fingers were detected by forexample any sensing mechanism 12 described herein, as being in dangerousproximity to the saw blade 304, the guard 308 would immediately coupleto the saw blade 304 causing the guard 308 to move clockwise along withthe saw blade 304. As the guard 308 closes any objects that are in closeproximity to the saw blade 304 are pushed along, and away from dangerouscontact with the saw blade 304. It will be appreciated that trigger 306may alternately engage teeth 320. Safety mechanism 14 j may be used inconjunction with any of the sensing mechanisms 12 disclosed herein.

[0204]FIG. 25 shows an exemplary miter saw 10 k which may employ asafety mechanism 14 k in accordance with the present invention. Safetymechanism 14 k alerts the operator of possible contact with saw blade330. Safety mechanism 14 k includes a plurality of flexible wireelements 332 extending from the center of saw blade 330. As saw blade330 is rotated, flexible wire elements 332 are positioned radiallyoutward by centrifugal force to form a circular pattern around therotating saw blade 330. If the operator of the power tool makes contactwith the flexible wire elements 332, the user is alerted that therotating saw blade 330 is in close proximity.

[0205] Moving Hands Away Without Inertia

[0206] An alternative to stopping the active portion of the power toolis to move the portion of the operator's body that is in dangerouslyclose proximity to the active portion of the power tool away from thepower tool. This methodology does not require a reaction system thatmust account for the forces associated with stopping a rotating object.However, like a braking system, a hand retraction system must performthe function of moving a portion of the operator's body away from adangerous position with the active portion of the power tool in a veryrapid period of time. In devices such as saws where rapid workpiece feedrates are possible, the portion of the operator's body must be movedaway from the active portion of the power tool very rapidly to preventand/or reduce injury.

[0207]FIGS. 26a and 26 b illustrate a safety mechanism 141 for rapidlymoving the hand of the user away from a rotating blade 340. Thrust bar342, is generally composed of a first gear 344 rotating with the sawblade 340 and a second gear 346 selectively intermeshed with the firstgear 344. In addition, a link bar 350 extends beyond the perimeter ofthe saw blade 340 positioned adjacent thereto. If a dangerous conditionis detected by for example one of the sensing mechanisms 12 disclosedherein, and it is desirable to move the hand of the operator rapidlyaway from the saw blade 340, a pin 352 thrusts second gear 346 and linkbar 350 into the second first gear 344. The link bar 350 consequentlyrotates in the opposite direction (arrow 354) as the blade 340 from aposition as shown in FIG. 26a to a position shown in FIG. 26b in orderto contact the hand of the operator and prevent prolonged contact withthe saw blade 340. It will be understood that alternate gearingconfigurations may be employed having other engaging alternatives whilereaching similar results.

[0208]FIG. 27 shows a safety mechanism 14 m operatively associated withtable saw 10 m. Safety mechanism 14 m includes a kerf guard 370 forpreventing contact between a user and the blade 376 of a table saw 10 m.Kerf guard 370 is composed of a kerf plate 372 and an actuationmechanism 374. In operation, if it is sensed (by for example one of thesensing mechanisms 12 disclosed herein) that a portion of the user'sbody is in close proximity to the saw blade 376, the kerf plate 372 isdriven from a position diagrammatically shown in FIG. 28 upward to aprotective configuration as shown in FIG. 29. This configurationprevents the operator from contacting the blade 376 of the saw 10 m. Asshown in FIGS. 28 and 29, actuation mechanism 374 includes cylinders 380having shafts 382 which linearly expand therefrom. Shafts 382 may beinfluenced into a position shown in FIG. 29 by springs, explosives,fluids or other means. It is readily appreciated that actuationmechanism 374 may alternatively include other fast acting actuationmechanisms such as hydraulic actuators, rack and pinion actuators or anyother sufficient mechanism.

[0209]FIGS. 30-32 illustrate a safety mechanism 14 n for rapidly movingthe hand of the user away from a rotating blade, hinge bar 384. Hingebar 384 is composed of a U-shaped bar positioned around the center of asaw blade 386 and having the distal ends 388 of the bar 384 attached athinge 396 to a portion 360 of the saw 10 n. The proximal portion 390 ofthe U-shaped member is oriented to oppose the distal hinged ends 388.Mounted near the distal ends 388 of hinge bar 384 is an electronicallyactivated charge module 392. Although it is shown that charge module 392is mounted near hinge 396, it will be appreciated that charge module 392may be mounted in any adequate position adjacent to the top of hinge bar384 sufficient to force hinge bar 384 downward.

[0210] The operation of safety mechanism 14 n will now be described ingreater detail. If it is determined by for example one of the sensingmechanisms 12 disclosed herein that a dangerous condition exists, charge392 is electrically activated. Once the charge 392 has been activated,hinge bar 384 is rapidly driven downward by the force of the charge(from a position diagrammatically depicted in FIG. 30 to a positiondiagrammatically depicted in FIG. 31). In this way, hinge bar 384 swingsin a direction identified by arrow 394 about hinge 396. Consequently,hinge bar 384 contacts the table portion 398 of saw 10 n oralternatively the work-piece 418 thereby displacing saw blade 386 in anupward direction identified by arrow 420 about hinge 422.

[0211] With continued reference to FIGS. 30 and 31 and continuedreference to FIG. 32, the orientation of bar 384 will be described. Bar384 is preferably positioned below arbor 424 and inner and outer bladeclamps 426, 228. In this regard, bar 384 may swing unimpeded from hinge396.

[0212] It will be appreciated that hinge bar 384 may alternativelycomprise different geometries or be arranged in other locations on saw10 n while reaching similar results. Furthermore, charge 392 mayalternatively comprise other mechanical or electrical configurationsadequate to deploy arm 384 downward with significant force to urge sawblade 386 upward about pivot 422.

[0213]FIGS. 33 and 34 illustrate a safety mechanism 14 p shownoperatively associated with saw blade 430. Saw blade 430 is shownremoved from a miter saw. Safety mechanism 14 p includes an inflationdevice 432 and an air bag housing 434 for housing air bag 436. Air bag436 is deployed from housing 434 by inflation device 432 upon sensing ofa dangerous condition by for example one of the sensing mechanisms 12disclosed herein for rapidly moving the hand of the user away from therotating blade 430. Air bag 436 is composed of a rapidly inflatablevessel that is positioned adjacent to the saw blade 430. If it isdesirable to move the hand of the user away from the saw blade 430,inflation device 432 rapidly inflates air bag 436 that expands outwardfrom a position shown in FIG. 33 to a position shown in FIG. 34 to drivethe hands of the user away from the blade 430. Alternatively, a secondinflation device 432 and air bag 436 may be concurrently employed withsafety mechanism 14 p. As a result, an air bag 436 may be placedproximate both sides of saw blade 430 to achieve more uniform push.

[0214]FIG. 35 illustrates a safety mechanism 14 q for rapidly moving thehand of the user away from a rotating blade 444. Safety mechanism 14 qincludes a charge 446 that is mounted to the lower guard 448 of a mitersaw 10 q. It will be appreciated that safety mechanism 14 q may also beused with a portable circular saw or other saws employing a guard. Thecharge 446 is of the electrically activated type and is oriented to firefrom the rear of the saw 10 q to the front of the saw 10 q. It will beappreciated that charge 446 may alternatively be an explosive device orother suitable device sufficient to move guard 448. If it is determinedby for example one of the sensing mechanisms 12 disclosed herein, that adangerous condition exists, charge 446 is operated. Charge 446 rapidlypropels the lower guard 448 clockwise from an open position (asdiagrammatically depicted in FIG. 35) to a closed position (asdiagrammatically depicted in FIG. 36) to prevent user contact with aportion of saw blade 444.

[0215]FIG. 37 illustrates a safety mechanism 14 r shown associated withmiter saw 10 r for rapidly moving the hand of the user away from arotating blade 470. Safety mechanism 14 r includes auxiliary upper guard462 rotatably coupled to saw 10 r by way of hinge 464 at the rear of saw10 r. Guard 462 extends around the front of the saw 10 r and includes adownward firing charge device (not specifically shown) mounted thereto.The firing device may include for example an electrically actuatedcharge similar to charge 446 used in relation to safety mechanism 14 q.Alternately, a torsion spring may be implemented at hinge 464 foractuating auxiliary guard 462 from a position shown in FIG. 37 to aposition shown in FIG. 38. In this regard, if a dangerous condition isdetected by for example one of the sensing mechanisms 12 describedherein, the firing device fires causing the auxiliary guard 462 torotate downward from a position diagrammatically shown in FIG. 37 to aposition diagrammatically shown in FIG. 38, moving the operators handaway from the saw blade 470 to prevent further contact therewith. Itwill be appreciated that auxiliary upper guard 462 may comprisealternative shapes which cooperate with a given saw provided guard 462may move unimpeded from an open position (away from a workpiece 476) toa position sufficient to block human interaction with blade 470.

[0216]FIGS. 39a and 39 b illustrate a safety mechanism 14 s shownassociated with miter saw 10 s for rapidly moving the hand of the useraway from a rotating blade 502. Safety mechanism 14 s includesprojectile magnet 504. Projectile magnet 504 is deployed from a largeelectromagnet 506 positioned above the front portion of the blade 502.Projectile magnet 504 is coupled to a rigid portion of saw 10 s such asguard 508 or the frame of the saw 10 s whereby it may be sufficientlyaimed toward the saw blade 502 and workpiece 510 interface. If it isdetermined by for example one of the sensing mechanisms 12 disclosedherein, that a dangerous condition exists, the polarity of theelectromagnet 506 is switched to force the projectile magnet 504downward in the direction of arrow 516. The force of the electromagnet506 and the gravitational forces combine to increase the momentum of theprojectile magnet 504. During operation, the projectile magnet 504 movesfrom a position adjacent to electromagnet 506 downward (arrow 516) to aposition as shown in 39 b to engage the hand of the user. Once theprojectile magnet 504 contacts the hand of the user, the momentum of themagnet 504 will drive the hand of the user away from the blade 502.

[0217] Moving Blade Away With Inertia

[0218]FIG. 40 is an illustration of a safety mechanism 14 t configuredto stop a saw blade of a table saw and effectively manage theconservation of momentum associated with rapid deceleration. As shown inFIG. 40, a safety mechanism 14 t is shown to include a frame 520, acollar 522 interconnected to frame 520 by a spring member 524, and ablade stop 526. Frame 520 is operatively connected to the table saw (notspecifically shown) at point 528 by way of a fastener and throughgearing 530 for selective rotation of safety mechanism 14 t about arbor536 through an infinite number of angles corresponding to an infinitenumber of positions for saw blade 534. In operation, if a dangerouscondition is detected by for example one of the sensing mechanisms 12disclosed herein, worm gear 540 is actuated allowing teeth 542 to urgegearing 530 toward a counterclockwise rotation. Worm gear 540 may beactuated by for example an electric motor. As a result, blade stop 526is actuated counterclockwise thereby allowing foot 546 to engage sawblade 534. Once saw blade 534 has been engaged, the rotational inertiaof saw blade 534 is transferred to linear inertia in the downwarddirection. The linear inertia drives collar 522 in a downward directionaway from the user and possible additional contact with the operator.Spring member 524 is also forced downward to absorb and dissipate aportion of the linear inertia in a controlled manner. Although springmember 524 is depicted as a single leaf spring, it is appreciated thatadditional leaf springs may be employed or alternatively other biasingmembers that may provide a force dissipating function in addition toinhibiting twisting motion between the axis defined by arbor 536 andjoint 532.

[0219] Turning now to FIGS. 41 and 42, a safety mechanism 14 u includinga ratcheting head 550 is shown. As will be described in greater detail,ratcheting head 550 actuates to prevent contact of the user with the sawblade 552. Ratcheting head 550 is composed of a saw guard 554, aratcheting handle 556 and a stop 558. Saw guard 554 includes a gearingportion 560 rotatably attached to the frame of the saw about a fastener562. Stop 558 is positioned along the top front of the saw blade 552,which is rotating clockwise. Ratcheting handle 556 includes a ratchetinggearing portion 548 that is intermeshed with gearing portion 560. Inoperation, if a dangerous condition is detected by for example one ofthe sensing mechanisms 12 disclosed herein, stop 558 engages blade 552.The rotational inertia of the rotating saw blade 552 causes the sawguard 554 to be translated upward from a position diagrammaticallydepicted in FIG. 41 to a position diagrammatically depicted in FIG. 42.As guard 554 is translated upward, the gearing portion 560 operativelyengages the ratcheting gearing portion 548 of handle 556. The ratchetingof gearing portion 560 locks the saw guard 554 at it's highest positionand prevents the saw blade 552 from coming in contact with the operatorshand. Although not specifically shown, it is appreciated that gearingportion 550 is coupled to the frame of a miter saw and cooperates withthe frame to translate downward to a position shown in FIG. 42.

[0220] As shown in FIGS. 43 and 44, safety mechanism 14 v is shown.Safety mechanism 14 v includes a strap deployment mechanism 560.Deployment mechanism 560 includes a strap 562 made of a durable materialsuch as Kevlar. Strap 562 passes through a moveable clutch 564 disposedin a housing arm 566. Clutch 564 is compressed onto the strap 562 with aseries of biasing members 578. Biasing members 578 are preferablysprings adequate to pinch the strap 562 with sufficient force such asbelleville springs. Strap 562 includes an adequate amount of slackcoiled within housing 566 to accommodate a deployment event as will bedescribed in greater detail. Strap 562 is guided through an actuatormount 568 whereby a spring 570 bounds the strap on an upper side. Spring570 is retained in an upward position on an opposite end by a release572. In this regard, strap 562 also is displaced toward release 572.Release 572 is supported for linear movement by a guide 574. A coil 580is disposed in housing 566 adjacent release catch 584. Release catch 584includes a magnet fastened thereon for communicating with coil 580. Inaddition, magnets 582 are disposed in housing 566 to attract catch 584in an at rest position (FIG. 43).

[0221] Extension arm 586 is coupled at a dovetail 590 on housing 566.Dovetail 590 allows housing 566 to be easily replaced. Extension arm 586is mounted to trunnion 591 at joint 588. A movable arm 592 extends fromtrunnion 591 and connects at actuator mount 568. The operation of safetymechanism 14 v will now be described. If a dangerous condition isdetected by for example one of the sensing mechanisms 12 disclosedherein, a signal is sent to coil 580. Coil 580 then builds a counterflux opposing magnets 582. The flux pushes the release 572 to the left(from a position diagrammatically depicted in FIG. 43 to a positiondiagrammatically depicted in FIG. 44). The spring 570 with the strap 562releasably attached is rapidly deployed downwardly past the periphery ofthe blade 594. Strap 562 is caught by the teeth of blade 594. Therotation of the blade 594 (clockwise as viewed from FIG. 43) pulls thestrap 562 around its perimeter further engaging additional teeth todistribute the force to stop blade 594. Clutch 564 is concurrentlyengaged providing a clamping force. As blade 594 rotates and pulls anyslack up due to the angle of the arm when spring 570 is deployed, thestrap 562 begins to slide through the clutch 564 with a constant forceto decelerate blade 594. After blade 594 is stopped, the user mustreplace the deployment mechanism 560. As such, the housing 566 is slidlaterally out of dovetail 590 and 598. The assembly of clutch 564 andbellows 596 is then replaced.

[0222] Turning now to FIGS. 45 and 46, a safety mechanism 14 w includinga shuttle stop 610 is shown. Safety mechanism 14 w is shown inconjunction with a miter saw 10 w. As will be described in greaterdetail, shuttle stop 610 is projected into rotating blade 612 to stopits rotation and thereby prevent contact of the user with a rotating sawblade 612. Safety mechanism 14 w includes a housing 614 having an upperchamber 616 and lower chamber 618. A fuse member 620 is positioned inthe upper chamber 616. Shuttle stop 610 is positioned in the lowerchamber 618 and connected to the frame of the saw 10 w by a strap 622. Astop pin 624 connects the fuse 620 and the biased shuttle 610 together.Shuttle 610 is positioned so that the leading edge is adjacent to theupper rear portion of the clockwise rotating saw blade 612. A truss 634extends from a table portion 636 and supports horizontal support arm638. Guard 640 extends over saw blade 612.

[0223] The operation of safety mechanism 14 w will now be described ingreater detail. If a dangerous condition is detected by for example oneof the sensing mechanisms 12 disclosed herein, a high current charge issent to fuse 620 by control 628. As fuse 620 is blown, stop pin 624,which was retained by fuse 620 is urged upwards by biasing member 630from a position diagrammatically depicted in FIG. 45 to a positiondiagrammatically depicted in FIG. 46. Once the lower portion of the stoppin 624 has cleared the top of shuttle 624, the shuttle 624 is driveninto the rotating teeth of the saw blade 612 (see FIG. 46) by biasingmember 642. It will be appreciated that other force transfer mechanismsmay be employed to urge shuttle 610 toward blade 612 such as but notlimited to an explosive charge.

[0224] Upon deployment, strap 622 uncoils from reel 632 as the teeth ofsaw blade 612 grasp the shuttle 610 and force the shuttle 610 clockwisearound the perimeter of the blade 612, creating tension on strap 622.Roller 644 guides shuttle 610 toward blade 612 during a deploymentevent. In addition to rapidly decelerating saw blade 612, as strap 622is stretched to a maximum distance, the head of the saw 10 w is drivenupward about pivot by the transfer of the rotational inertia to linerinertia, moving away from the user.

[0225] As shown in FIGS. 47a and 47 b a safety mechanism 14×including acable stop 646 is shown associated with miter saw 10×. Again, althoughsafety mechanism 14×is shown associated with miter saw 10×, other powertools may be employed while reaching similar results. Cable stop 646includes a cable 648 having an engagement member 650 coupled thereto. Afirst end of cable 648 is coupled at attachment 654 on the upper portionof arm 652. Cable 648 is routed around the rear of arm 652.

[0226] The operation of safety mechanism 14×will now be described. If adangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, engagement member 650 is fired upwardinto a gap defined by the space between blade 656 and support 658.During normal operation, blade 656 rotates in a clockwise direction asviewed from FIGS. 47a and 47 b. As a result, the teeth of blade 656grasp engagement member 650 thereby pulling cable 648 in a directioncounterclockwise around the rear portion of arm 652. Once the slack ofcable 648 is used, cable 648 pulls arm 652 at attachment 654 therebyurging arm 652 upward around pivot 660 from a position asdiagrammatically depicted in FIG. 47a to a position as diagrammaticallydepicted in FIG. 47b.

[0227] It will be appreciated that engagement member 650 mayalternatively be fired by other means such as but not limited to anexplosive device or mechanical assembly. Engagement member 650 ispreferably comprised of a hard pliable material such as hard plastic forexample. It will also be appreciated that cable 648 may also be routedaround an additional pivot point which may comprise a swing arm mountedon support 658.

[0228] Turning now to FIGS. 47c and 47 d, a safety mechanism 14 yemploying a leaf spring stop 664 is shown operatively associated withmiter saw 10 y. Leaf spring stop 664 includes a leaf spring 666, andcable 668. Leaf spring 666 is disposed around a mounting hub 670proximate to the perimeter of saw blade 672. Cable 674 is coupled ateyelet 676 and biases leaf spring 666 in a direction away from saw blade672. Deployment actuator 690 is coupled (not specifically shown) to aportion of the miter saw 10 y and maintains adequate tension on cable674 during normal operation. Strap 678 is coupled to leaf spring 666, ona first end and is mounted to support 680 at spool 682 on an oppositeend. A friction device 684 includes friction block 688 urged against anupper portion of support 680 by biasing member 686. In this way,friction device 684 provides smooth deployment of strap 678 whiledissipating much of the stopping energy during a stopping event as willbe described in greater detail.

[0229] If a dangerous condition is detected by, for example one of thesensing mechanisms 12 disclosed herein, deployment actuator 690 releasescable 674. Deployment actuator 690 may comprise any adequate releasingmeans such as but not limited to a coil and magnet configuration asdiscussed in safety mechanism 14 v or a fuse and stop pin configurationas discussed in safety mechanism 14 w. Upon release of cable 674, leafspring 666 displaces toward rotating saw blade 672 causing the teeth ofsaw blade 672 to pierce strap 674. In turn, saw blade 672 pulls strap674 in a clockwise direction unraveling spool 682. Friction device 684slows the travel of strap 674 until saw blade 672 comes to a completestop.

[0230] Moving Blade Away Without Inertia

[0231] Turning now to FIGS. 48-50, a safety mechanism 14 aa is shown.Safety mechanism 14 aa is illustrated in cooperation with a table saw 10aa. Safety mechanism 14 aa includes a displacement mechanism 710 forurging saw blade 712 downward to a position below opening 714 of tablesurface 716. Displacement mechanism 710 includes a sufficientdisplacement means such as, but not limited to, an electronic charge, ora mechanical actuator for example. It will also be appreciated thedisplacement mechanism 710 may alternatively be placed below hub 720 ofblade 712 for attracting blade 712 toward the displacement mechanism710. Such a configuration may include, but is not limited toelectromagnets placed at the displacement mechanism 710 and at the sawblade hub 720.

[0232] During operation, if a dangerous condition is detected, by forexample on of the sensing mechanisms 12 disclosed herein, displacementmechanism 710 is actuated. As a result, saw blade 710 moves from aposition diagrammatically depicted in FIG. 49 to a positiondiagrammatically depicted in FIG. 50. While not specifically shown, itis appreciated that the support structure operatively engaged to blade712 includes vertical displacement ability to accommodate the verticaltravel of blade 712 during a retraction event.

[0233] Referencing now FIGS. 51 and 52, a safety mechanism 14 bb isshown operatively associated with miter saw 10 bb. Safety mechanism 14bb shows a blade retraction and stop mechanism, linkage 730, thatprevents contact of the user with the saw blade 728. Linkage 730 iscomposed of a saw arm 732, a saw stop 734, a frame 735, a stabilizinglink 736 and a brake link 738. Frame 735 is a generally upwardlyextending member having a first and a second attachment points.Connected to the first attachment point is the first end of saw arm 732.The other end of saw arm 732 is connected to a saw blade 728. Connectedto the second attachment point is brake link 738. Brake link 738 isinterconnected to saw arm 732 through stabilizing link 736 and includesa saw stop 734 attached to a distal end.

[0234] In operation, if a dangerous condition is detected by for exampleone of the sensing mechanisms disclosed herein, the saw stop 734 isactuated toward the rotating blade 728 to stop the rotation thereof. Sawstop 734 may be actuated by adequate means such as, but not limited to amechanical actuator, or may alternatively be gravity induced forexample. Once the saw stop 734 engages saw blade 728, the rotationalinertia of saw blade 728 is transferred to linear inertia, driving thesaw blade 728 upward. The saw arm 732 and brake link 738 are drivenupward and away from contact with the user. It will be appreciated thatalthough linkage 730 is depicted as a four bar mechanism, other linkagesmay be employed yielding similar results.

[0235] Turning now to FIGS. 53 and 54 a safety mechanism 14 cc is shown.Safety mechanism 14 cc is shown operatively associated with miter saw 10cc. Safety mechanism 14 cc includes a deployment mechanism 740 foradvancing arm 742 and therefore saw blade 744 of saw 10 cc upward andaway from contact with a user. Deployment mechanism 740 is preferablydisposed on the base 748 of table portion 750 adjacent hinge 752.

[0236] Deployment mechanism 740 may include any sufficient mechanismcapable of displacing arm 742 about pivot 752 such as, but not limitedto, an explosive device, a mechanical spring, compressed gas or thelike. In operation, if a dangerous condition is detected, by for exampleone of the sensing mechanisms 12 disclosed herein, deployment mechanism740 is actuated. As such, the force generated onto arm 742 urges arm 742upward about pivot 752 from a position diagrammatically depicted in FIG.53 to a position diagrammatically depicted in FIG. 54.

[0237] Engaging the Blade With a Pawl Stop

[0238]FIG. 55 provides a fragmentary view of a safety mechanism 14 ddthat may be adapted for use with a power tool. The safety mechanism 14dd includes a pawl 754 pivotally coupled to the housing 760 of the powertool and a biasing device 756 operably coupled to the pawl 754. As willbe further described below, the safety mechanism 14 dd is operable toengage and thus stop the rotary motion of the saw blade 758. While thefollowing description is provided with reference to a safety mechanism14 dd, it is readily understood that the pawl of the present inventionmay be adapted for use with different types of braking mechanisms and/orpower tools.

[0239] More specifically, the pawl 754 is pivotally mounted to a frameportion 760 of the saw housing on an axle 762 that extends through abore 764 formed in the frame portion of the housing 760. The pawl 754 isadapted to pivot into the teeth 766 of the blade 758 under the influenceof biasing mechanism 756. In a preferred embodiment, the biasingmechanism 756 is a helical compression spring. Additionally, the pawl754 is adapted to be self locking, i.e., draw into tighter engagementwith the teeth 766 of the blade 758 due to the relative geometry of theblade 758 and pawl 754 as they are drawn together.

[0240] In a first preferred embodiment, the pawl 754 is composed of amain body portion 770 and a contact portion 772. The main body portion770 defines the structure of the pawl 754 and adds to the rigidity ofthe structure. The main body portion 770 of pawl 754 is preferablyconstructed of a polymeric material having a relatively high hardness,such as acrilonitrile-butadiene-styrene (ABS). However, it iscontemplated other materials having suitable physical properties may beutilized to form the main body portion 770 of pawl 754.

[0241] The contact portion 772 is formed opposite bore 764 on the pawl754 and is proximate to the teeth 766 of saw blade 758. The contactportion 772 of pawl 754 is preferably constructed of an elastomericmaterial, such as polyurethane. However, it is contemplated othermaterials having suitable physical properties may be utilized to formthe contact portion 772 of pawl 754.

[0242] When a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein, and it is desirable to stopblade 758, pawl 754 is rotated into engagement with the teeth 766 ofblade 758 by influence from biasing mechanism 756. Contact portion 772of the pawl 754 engages the blade 758 initially. The elastomericmaterial of contact portion 772 grasps the blade 758 due to its inherentmaterial properties such as a relatively low shear modulus. As the teeth766 of the blade 758 grasp the contact portion 772 of the pawl 754, theblade 758 begins to slow down. As the blade 758 is drawn into furtherengagement with the contact portion 772 of the pawl 754, the blade 758is increasingly slowed. If blade 758 is not completely slowed by thecontact portion 772 of pawl 754, teeth 766 will engage a plurality ofinterlocking features 774 formed on main body portion 770. Interlockingfeatures 774 extend outward from the main body portion 770 towardcontact portion 772. As noted above, the main body portion 770 of pawl754 is preferably constructed of a polymeric material having relativelyhigh hardness. Therefore, as the blade 758 engages the interlockingfeatures 774 of the pawl 754, the relative hardness of the polymericmaterial forming the interlocking features 774 will significantly slowand stop blade 758. In this way, the improved pawl 754 of the presentinvention employs the physical properties of two materials to slow therotation of the blade 758.

[0243] Interlocking features 774 also increase the surface area betweenthe contact portion 772 and the main body portion 770 for purposes ofadhesion. In a preferred embodiment, interlocking features 774 of thepawl 754 are constructed in series of channels extending perpendicularto the plane defined by blade 758. However, it is appreciated thatinterlocking features 774 may be constructed in many different forms andnot depart from the scope of the present invention.

[0244] Additionally, it is preferred that contact portion 772 be formedby an overmolding process. In an overmolding process an elastomericmaterial is injected onto a plastic body (main body portion 770).Overmolding allows the two materials (the elastomeric material and theplastic body) to be cohesively attached. Therefore, no external adhesiveor fasteners are required.

[0245] An alternative preferred embodiment for a safety mechanism 14 dd′is shown in FIG. 56 wherein like components are referred to with likereference numbers. Safety mechanism 14 dd′ includes an improved pawl754′. In this embodiment, the pawl 754′ is formed as a unitary structureby injection molding of an elastomeric material 778 such aspolyurethane. It is contemplated that pawl 754′ may be formed of otherelastomeric materials and not depart from the scope of the presentinvention. In forming pawl 754′ through injection molding, it isdesirable that the configuration of the mold be such that the fill(flow) path of the injected plastic is perpendicular to the directionthat the pawl 754′ will engage saw 758. The direction of the fill pathis indicative of the direction that most of the polymer chains areoriented. As a result, the material having a fill path that isperpendicular to the direction of impact will have an increased impactstrength, thereby improving the ability of the pawl to slow and/or stopthe rotation of the blade 758.

[0246] It is envisioned that the pawl 754′ may further include a fibrousmaterial such as, but not limited to glass, graphite or KEVLARcoinjected with the elastomeric material 778 to form a fiber reinforcedplastic. In this form, both the fibrous material and the elastomericmaterial retain their physical and chemical identities, yet produce acombination of properties that cannot be achieved by either of themindividually. In a fiber reinforced plastic, the fibrous material is theprincipal load carrying members, while surrounding elastomeric material778 keeps the fibrous material in the desired position and orientation.The elastomeric material 778 acts as a load transferring medium betweenthe fibers and also protects them from environmental damage.

[0247] In fiber reinforced plastics, the fibers can be materials thatare long directional filaments, particles that are small non-directionalchunks or whiskers that are small directional filaments. In general,fibers tend to have very long lengths with respect to the surroundingmaterial, and tend to have a significantly higher strength along theirlength. Preferably, fibrous materials include glass fiber, carbon fiber,and kevlar fiber. However, other types of fibrous materials are alsowithin the scope of the present invention.

[0248] When it is desirable to stop blade 758, pawl 754′ is rotated intoengagement with the teeth 766 of blade 758 by influence from biasingmechanism 756. As pawl 754′ engages blade 758, the elastomeric material778 grasps the teeth 766 of blade 758 due to its relatively high elasticmodulus and relatively low shear modulus. As the teeth 766 grasp thepawl 754′, the blade 758 begins to slow down and is drawn into furtherengagement with the pawl 754′. As teeth 766 of blade 758 engage pawl754′, the fibrous material also engages teeth 766 of blade 758. As teeth766 engage the fibrous material, the speed of blade 758 is increasinglyslowed due to the relatively high strength of the fibrous material. Thecomposite structure of pawl 754′ effectively engages blade 758 throughelastomeric material 778 and effectively slows and stops blade 758through the fibrous material.

[0249] Referencing now FIGS. 57 and 58, a safety mechanism 14 eeincluding an alternate pawl 780 is shown. The operation of safetymechanism 14 ee is preferably employed similar to safety mechanism 14dd. Pawl 780 is comprised of a carrier 782 and an engagement portion784. Engagement portion 784 is preferably made of a thermoplastic withhigh yield strength, but also a high percent elongation to allow it tostretch as it absorbs the energy from the saw blade 786 during a stopevent. The material of engagement portion 784 is also conducive toabsorb the initial impact of blade 786 while promoting uniform stoppingtimes regardless of blade tooth geometry. Carrier 782 is comprised of arigid lightweight material such as, but not limited to, rigid plastic.Carrier 782 is preferably a material conducive to minimize systeminertia to facilitate rapid release of the safety mechanism 14 ee andalso provide necessary strength to maintain engagement portion 784 infirm contact with blade 786. The two piece pawl (i.e. one part carrier782 and one part engagement portion 784) allows the user to remove theengagement portion 784 from carrier 782 after a stop event and replaceit with a new engagement portion.

[0250] Pawl Activation

[0251]FIGS. 59a-61 illustrate exemplary activation systems for deployinga pawl type braking system, such as disclosed herein, upon a rotatingsaw blade. In general, the activation systems include a biasing memberurging the pawl into contact with the active portion of the power tooland a release mechanism coupling the pawl to a portion of the power tool12. The activation system is actuated upon signaling from a sensingmechanism such as described herein, that a dangerous condition exists.In this way, the pawl is uncoupled from a secure position and urged intoengagement with the active portion of the power tool to prevent orreduce possible injuries caused by contact between a portion of theoperator's body and the active portion of the power tool. While theactivation system described herein is shown employing a pawl type stop,it is appreciated that other types of stops adapted to engage the activeportion of a power tool may be utilized with the activation system ofthe present invention.

[0252] Turning now to FIGS. 59a and 59 b, a safety mechanism 14 ffemploying a magnetic pawl release 802 is shown. Magnetic pawl release802 includes a biasing member 804 for exerting a biasing force on pawl806 to urge pawl 806 toward the active portion of the power tool. Thebiasing member 804 of the present invention is preferably a compressionspring that is positioned between a portion of the power tool 10 ff suchas frame 810 and an opposing face 808 of pawl 806. It is alsocontemplated that other types of biasing members such as leaf springsmay be utilized to urge the pawl into engagement with the active portionof the power tool. Also, it is appreciated that the biasing member maypositioned in a variety of positions and still urge the pawl 806 intoengagement with the active portion of the power tool 10 ff such as a sawblade.

[0253] The release mechanism 802 is comprised of a first and secondoppositely charged magnets 814, 816 attached to the pawl 806 and aportion of the power tool 810, respectively. The first magnet 814 ispreferably coupled to the rear surface of the pawl 806 and extends in agenerally parallel direction with respect to the rear surface of thepawl 806. The second magnet 816 is attached to a portion 810 of thepower tool 10 ff and preferably extends generally parallel to the firstmagnet 814 when the pawl 806 is in the secured position (FIG. 59a). Inthis manner, the face of the second magnet 816 is positioned to alignsubstantially with the face of the first magnet 814 when the pawl 806 isin the secured position to optimize the attraction therebetween. Thefirst and the second magnets 814, 816, due the opposite polarities, areattracted to one another and provide a second biasing force that isopposite in direction and at least as large in magnitude as the biasingforce of the biasing member 804.

[0254] The second magnet 816 also includes a coil 820 formed fromelectrically conductive wire disposed around the outer surface of themagnet 816. The coil 820 is coupled to a power source (not specificallyshown) for controlling the magnetic force of the second magnet 816 as iswell known in electromagnetics.

[0255] When a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein, and it is desirable to activatethe pawl 806 to stop the active portion of the power tool, an electricalvoltage is applied to the wire 820. As the electrical charge is applied,the attractive force of the second magnet 816 is decreased. Once theattractive force of the first and the second magnets 814, 816 is lessthan the biasing force of the biasing member 804, the pawl 806 isreleased from the secured position (as diagrammatically depicted in FIG.59a) into an engaging position (as diagrammatically depicted in FIG.59b) with the active portion of the power tool 10 ff.

[0256] The amount of time required to release the pawl is preferablyminimized to reduce the overall time required to stop the active portionof the power tool 10 ff. Therefore, it is desirable to apply a largeelectrical charge to the second magnet 816 to allow the attractive forceto be rapidly reduced or eliminated. It is also appreciated that anelectrical charge capable of changing the polarity of the second magnet816 could be applied to the second magnet 816 causing the first and thesecond magnets 814, 816 to have a repulsion force, further reducing theperiod of time required release the pawl 806.

[0257] Sensor 822 of the present invention determines if the pawl 806 isin the secured position and if the coil 820 can be energized. The sensorshown in FIGS. 59a and 59 b is a Hall-type sensor. The Hall sensormeasures the magnetic induction field applied in relation to the currentflow. Thus, the Hall sensor determines the amount of attraction forcesbetween the first and the second magnets 814, 816 to determine, if thepawl 806 is in place and if the coil 820 can be energized. It isappreciated that other sensors may be employed within the scope of thepresent invention.

[0258] In operation, a controller (not specifically shown) for the powertool measures the sensor 822 to determine the location and status of thepawl 806. If the pawl 806 is in the secured position, the controllerallows operation of the power tool 10 ff. In the event of a dangerouscondition, the controller applies an electrical charge to the coil 820of the second magnet 816. Once the coil 820 is electrically charged, theattractive force of the first and second magnets 814 and 816 is reducedand the biasing member 804 urges the pawl 806 into engagement with theactive portion of the power tool 10 ff in a relatively short period oftime.

[0259] Turning now to FIGS. 60a-60 c, a safety mechanism 14 gg employinga fuse member 830 is shown. Like components are referred to with likereference numbers as safety mechanism 14 ff. The safety mechanism 14 ggincludes a biasing member 804 urging the pawl 806 into contact with theactive portion of the power tool 10 gg and a fuse member 830 couplingthe pawl 806 to a portion of the power tool 10 gg. The safety mechanism14 gg is designed, upon detection of a dangerous condition by forexample one of the sensing mechanisms 12 disclosed herein, to uncouplepawl 806 allowing the pawl to engage the active portion of the powertool 10 gg to prevent or reduce possible injuries caused by contactbetween a portion of the operator's body and the active portion of thepower tool 10 gg. While the activation system of the present inventionis shown employing a pawl type stop, it is appreciated that other typesof stops adapted to engage the active portion of a power tool may beutilized with the activation system of the present invention.

[0260] Safety mechanism 14 gg including fuse member 830 extends frompawl 806 to a portion of the power tool 10 gg. The fuse member 830 isgenerally comprised of an electrically conductive wire 832 formed into aloop shape and a crimp portion 834 coupling the ends of the wiretogether. The loop shape of the fuse member allows the fuse to bepositioned around a desired point on each of the power tool 10 gg andthe pawl 806 as needed. The electrically conductive wire 832 is formedof a material that is deformable upon application of a relatively largeelectrical current to the wire 832. The crimp portion 834 is generally aunitary member that is positioned over the ends of the wire 832 anddeformed to mechanically couple the first and second ends of the wire832 together. The crimp portion 834 may be formed of any of a variety ofmaterials exhibiting greater strength than the wire 832.

[0261] When a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein and it is desirable to activatethe pawl 806, a relatively large electrical current is applied bycontroller 838 to the fuse member 830. Upon application of theelectrical current, the fuse member 830 begins to weaken mechanically.Once the biasing force of the biasing member 804 exceeds the tensilestrength of the electrified fuse member 830, the pawl 806 is urgedtoward the active portion of the power tool (FIG. 60b).

[0262] The electrical activation of the present invention allows therapid release of the pawl stop of the braking system. Rapid release ofthe pawl 806 reduces the overall time required to stop the activeportion of the power tool. Thus, the possibility for injurious contactbetween the active portion of the power tool and a portion of theoperator's body is reduced or eliminated.

[0263]FIGS. 61a-61 c illustrates a safety mechanism 14 hh including analternative fuse member 830′. Fuse 830′ includes a unitary stamped metalbody portion. Mounting bores 818 are disposed on opposite ends of fuse830′ for mounting to pawl 806 and tool 10 hh respectively. The operationof safety mechanism 14 hh is similar to the operation of safetymechanism 14 gg. Fuse 830′ presents several advantages over atraditional wire fuse. In this regard, no additional assembly is neededwith unitary fuse member 830′. In addition, the length of the fuse 830′is controlled by tooling rather than during assembly of the fuse 830′.

[0264] A second embodiment of a pawl type activation system is shown inFIGS. 62a-62 b. Safety system 14 ii includes a biasing member 840 urginga pawl 842 into contact with the active portion of the power tool and anactivation system 844 coupling the pawl 842 to a portion of the powertool. The safety system 14 ii is designed, upon signaling from forexample a sensing mechanism 12 disclosed herein, to uncouple the pawl842 allowing the pawl 842 to engage the active portion of the power toolto prevent or reduce possible injuries caused by contact between aportion of the operator's body and the active portion of the power tool.While the activation system 844 of the present invention is shownemploying a pawl type stop, it is appreciated that other types of stopsadapted to engage the active portion of a power tool may be utilizedwith the activation system of the present invention.

[0265] The activation system 844 includes a rotatable latch 846 engaginga finger portion 848 of the pawl 842 and first and second solenoids 850,852 actuating the latch 846. The latch 846 is rotatably coupled about anaxis of rotation to a portion of the power tool to support the latch 846and the pawl 842 in the secured position. The latch 846 includes anengagement arm 856, a support arm 858 and an activation arm 860extending generally from the axis of rotation in a “T” shapedconfiguration. The engagement arm 856 of the latch 846 operativelyengages finger portion 848 of the pawl 842. The support arm 858 engagesthe first solenoid 850 to restrain the pawl 842 in the secured positionvia the engagement arm 856. The activation arm 860 is in contact withthe second solenoid 852 which operatively rotates the latch 846 to allowthe pawl 842 to engage the active portion of the power tool.

[0266] The first solenoid 850 operates as a protective device to preventinadvertent activation of the pawl 842. In operation, the plungerportion 862 of the first solenoid 850 is placed in the extended positionto engage the support arm 858 of the latch 854 during the initialunstable operation of the power tool. The plunger portion 862 of thesolenoid 850 prevents the latch 854 from rotating and releasing theengagement arm 856 from engagement with finger 856 of the pawl 842.

[0267] Once the power tool has stabilized, the second solenoid 852 ismagnetically coupled to activation arm 860 by an electromagnet forpreventing rotation of the latch 854 and release of the pawl 842. Next,the plunger portion 862 of the first solenoid 850 is retracted. If adangerous condition has been detected by for example one of the sensingmechanisms 12 disclosed herein and it is desirable to release the pawl842, the magnetic coupling between the activation arm 860 and the secondsolenoid 852 is reduced. Once the magnetic coupling is reduced, latch846 rotates and the biasing member 840 urges the pawl 842 about pivot864 (from a position diagrammatically depicted in FIG. 62a to a positiondiagrammatically depicted in FIG. 62b) into engagement with the activeportion of the power tool. The electromagnetic coupling of the pawl 842allows the pawl 842 to be activated relatively rapidly. Rapid activationof the pawl 842 reduces the overall time required to stop the activeportion of the power tool. Thus, the period of time that injuriouscontact may take place between the active portion of the power tool anda portion of the operator's body is also reduced.

[0268] In the event of interruption to the electrical power of theactivation system 844 the pawl 842 will not engage the active portion ofthe power tool. Once electrical power is removed from the activationsystem 844, the plunger portion 862 of the first solenoid 850 willreturn to the extended position. In the extended position, the plunger862 prevents rotation of the latch 860, which will release the pawl 846.Once a deployment event has occurred, pawl contacts 866 detach fromtrigger printed circuit board 868. Pawl contacts 866 must be reattachedto trigger printed circuit board 868 after a deployment event.

[0269] Strap Stops

[0270] Braking systems are well known for use with many devices.Conventional braking systems either engage the portion of the devicethat is desired to be stopped or a segment of the device that isconnected to the portion of the device that is desired to be stopped.However, many braking systems require a lengthy period of time to stopthe portion of the power tool. Braking systems in power tools must beable to stop the active portion of the power tool in a very rapid periodof time to reduce and/or eliminated the amount of injury to the operatorof the power tool due the relatively high speeds of the power tool andthe dangerous nature of the active portion of the power tool.

[0271] Turning now to FIGS. 63a and 63 b, a safety mechanism 14 jjemploying a strap stop 870 is shown operatively associated with mitersaw 10 jj. The exemplary power tool embodied herein is a miter saw,however it is appreciated that the safety system of the presentinvention may be adapted for use with a variety of power tools. Ingeneral, miter saw 10 jj includes a strap 872 employed to providebraking force upon engagement with a saw blade not specifically shown.Strap 872 is preferably made of a strong flexible material such asKevlar. A friction stopping device 898 includes a friction disk 882 anddrum 876.

[0272] Housing 878 includes strap 872 shown wound around drum 876 whichis rotatably disposed on shaft 880. Strap 872 is wrapped around drum 876in sufficient supply to accommodate a single blade stop event. Frictiondisk 882 is fixed from rotation with drum 876. A spring 894 biasesfriction disk 882 into engagement with drum 876. In a safety event thestrap 872 is moved into engagement with a saw blade causing the strap872 to be pulled by the blade. As such, the strap 872 will uncoil fromdrum 876 as the drum 876 rotates in a counterclockwise direction asviewed from FIG. 63a. The friction disk 882 provides a predeterminedamount of friction to resist excessive rotation of the spool 876 in adeployment event. Friction disk 882 includes friction material disposedthereon for cooperating with biasing member 894 urging friction disk 882into drum 876. It is appreciated that alternatively or additionally,friction material may be incorporated on the engaged surface of drum876. Friction spool 876 is preferably placed in a location favorable tounabated unwinding. Accordingly, the friction provided by theinteraction between friction disk 882 and drum 876 generates the forcenecessary to stop rotation of the saw blade.

[0273] Deployment mechanism 900 includes carrier 902 supporting twoedges of the strap 872. The center of the strap 872 is unengaged andsuspended between the two edges 904. Edges 904 are secured in channelsproviding adequate resistance to the removal of the strap 872 laterallyor perpendicularly to the straps orientation. This resistance however isinsignificant relative to the friction provided by friction disk 882.

[0274] The strap carrier 902 is preferably deployed by one of thefollowing deployment means. A preferred embodiment includes a spring904, first and second magnets 906, 908 and a coil 910. The spring 904 iscompressed which provides the deployment force. First magnet 906 iscoupled to the strap carrier 902 and the second magnet 908 is coupled tothe housing 878. Second magnet 908 exerts sufficient attractive force onthe first magnet 906 to overcome the spring 904. The coil 910 is used todegrade the field in the fixed magnet 908 so that at the desired time,the spring force overcomes the magnetic force and the strap 872 moves upto engage the saw blade. Alternatively, the first and second magnet 906and 908 may be replaced with a fuse wire such as disclosed in relationto safety mechanism 14 w for example. While not specifically shown inrelation to this embodiment, a first end of the fuse wire may beattached to the strap carrier 902 and a second end attached at twoelectrical contact points on the housing 878. A small gap extendsbetween the two electrical contact points. When sufficient voltage isapplied at the two contacts, a large current is induced in the fuse wireheating and weakening the segment of wire between the contacts. Thespring force then breaks the fuse wire and the strap carrier 902 isreleased to engage the saw blade 874. It will be appreciated that otherdeployment mechanisms may be employed within the scope of the presentinvention.

[0275] When a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein, coil 910 degrades the magneticfield between magnets 906 and 908 allowing spring 904 to force carrier902 toward the saw blade into the direction depicted by arrow 912, andthus strap 872 into the saw blade. In this regard, the blade teethengage the center unsupported section of the strap 872 causing the bladeteeth to pierce the strap 872. Once the strap 872 is forcefully engagedto the blade teeth, the strap 872 is pulled out of the housing 878, theslack is used and the braking force generated by the friction clampingdevice 898 slows the blade 874 to a stop as the strap 872 unwinds fromdrum 876.

[0276] In an alternate embodiment shown in FIG. 63c, safety mechanism 14jj′ includes strap 872 routed through a freely pivoting frictionclamping device 884. Like reference numbers are used to designate likecomponents. Strap 872 is wrapped around spool 914. Clamping device 884includes a pivoting steel block 886 on a large shaft 888, such as 0.75inch diameter, with a plate 890 attached by conventional fasteners 892.The strap 872 is routed to pass between the plate 890 and the block 886.Plate 890 is secured to the steel block 886 with a predetermined amountof clamping force providing a frictional force to resist movement of thestrap 872 through clamp device 884. A sufficient amount of slack isarranged in the strap 872 enabling the strap 872 to be wrapped aroundthe blade 874 as necessary to generate a sound engagement between thestrap 872 and the blade teeth.

[0277] As with safety mechanisms 14 jj and 14 jj′, an adequate amount ofstrap 872 is wound around drum 876 and 914 to provide enough stoppingtravel. Furthermore, subsequent to a stopping event, strap 872 ispreferably replaced by an unused strap and recoiled through therespective stopping mechanisms 14 jj, 14 jj′.

[0278] Swing Blade Away From Contact

[0279] Referencing now FIGS. 64a-64 j, safety mechanisms 14 kk-14 ll′are described incorporating apparatus sufficient to displace a rotatingsaw blade and support arm about a pivot point on the saw structure. Theresulting motion causes the saw blade to swing upwards and out ofcontact with the user. Although the exemplary descriptions are directedtoward a miter saw, it will be appreciated that other power tools may beemployed within the scope of this disclosure.

[0280] Safety mechanism 14 kk as shown in FIGS. 64a and 64 b includesswing arm 920 having fore and aft finger supports 922 and 924respectively extending therefrom. Swing arm 920 is rotatably coupled atpivot gear 930 to frame 926 of miter saw 10 kk. Support bar 928 connectsfinger supports 922 and 924. Saw blade 932 is coupled to a distal end ofswing arm 920. Gear 934 is meshed for rotation with pivot gear 930 andcooperates therewith upon actuation of safety mechanism 14 kk during asafety event.

[0281] The operation of safety mechanism 14 kk will now be described ingreater detail. If a dangerous condition is detected by for example oneof the safety mechanisms 12 disclosed herein, gear 934 is activated in acounterclockwise direction (arrow 936). As a result, swing arm 920swings upward and away from contact with the user from a position asdiagrammatically depicted in FIG. 64a to a position as diagrammaticallydepicted in FIG. 64b. Gear 934 is preferably actuated with a motor (notspecifically shown) with sufficient speed to rotate swing arm and thussaw blade 932 out of contact with the user in a minimal amount of time.It will also be appreciated that meshed gears 934 and 930 may alsocomprise other explosive, mechanical or electromechanical devices withinthe scope of this invention.

[0282] Turning now to FIGS. 64c and 64 d, safety mechanism 14 kk′incorporating cable 938 is shown. Cable 938 includes a first end havinga loop 940 and an opposite end spooled around drum 942. An intermediateportion of cable 938 passes through friction device 944. Friction device944 includes a friction block 946 biased against support arm 948 bybiasing member 950.

[0283] If a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein, loop 940 of cable 938 is throwntoward rotating saw blade 952 by deployment module 954. In this way,loop 940 grasps the teeth of rotating saw blade 952 thereby uncoilingcable 938 from drum 942. Concurrently, friction device 944 slows themomentum of cable 938 allowing saw blade 952 to come to a complete stop.The angular momentum of rotating saw blade 952 causes arm 956 to rotateupward about pivot 958 from a position as shown in FIG. 64c to aposition shown in FIG. 64d. It will be appreciated that an adequateamount of cable is stored around drum 942 to sufficiently uncoil duringa stop event. Deployment module 954 may comprise any sufficient means tothrust loop 940 toward saw blade 952 such as but not limited to anexplosive firing device.

[0284]FIGS. 64e and 64 f illustrate safety mechanism 14 kk″ having analternative configuration from safety mechanism 14 kk′. As such, likecomponents will be referred to with like reference numerals. Frictiondevice 944′ is mounted for cooperation with arm 956′. Furthermore, drum942 is mounted at an upper portion of support arm 948′.

[0285] The operation of safety mechanism 14 kk″ is substantially similarto safety mechanism 14 kk′. The alternate placement of friction device944 and drum 942 provides different braking and packaging advantagesassociated with a given miter saw configuration.

[0286] With reference to FIGS. 64g and 64 h, safety mechanism 1411 willbe described in cooperation with miter saw 1011. Safety mechanism 1411includes deployment wedge 960 and magneto-rheological fluid shock 962.Deployment wedge 960 is preferably slidably coupled to arm 964. Arm 964is pivotally coupled to frame 966 at a first end and includes a sawblade 968 coupled at an opposite end.

[0287] If a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein, wedge 960 is deployed in adirection denoted by arrow 970 toward an upper portion ofmagneto-rheological shock 962. The force created from the impact ofwedge 960 into shock 962 causes rod 974 to expel from shock 962 causingarm 964 and thus saw blade 968 to swing upwardly about pivot 972. Uponarticulation of arm 964 about pivot 972, shock 962 expands from aposition as diagrammatically shown in FIG. 64g to a position asdiagrammatically shown in FIG. 64h. Once shock 962 has expanded to theposition shown in FIG. 64h, a current is applied to themagneto-rheological fluid within shock 962 causing the shock to lock inan expanded position. As is well known, a magneto-rheological fluiddamper utilizes a fluid which can have the viscosity altered through theapplication of a magnetic field. It will be appreciated that alternateconfigurations may be employed to maintain arm 964 in the position shownin FIG. 64h, for example, a master cylinder may be incorporated to filla reservoir within shock 962 to lock the arm in a safe position. Inaddition, a biasing swing arm may be incorporated to encourage retentionof cylinder 962 in an expanded position. In this way, a biasing swingarm may be employed between rod 974 and shock 962 to allow movement ofrod 974 out of cylinder 962 in a first expanded position and resistmovement of rod 974 back into shock 962.

[0288] Safety mechanism 14 ll′ incorporated into saw 10 ll′ is depictedin FIGS. 64i and 64 j and includes expansion shock 976. Expansion shock976 includes first and second extension rods 980 and 982 selectivelyextending therefrom. Expansion shock 976 is pivotally coupled to arm 978at pivot 984. During a safety event, rod 982 is expelled from rod 980thereby rotating arm 978 and thus saw blade 986 up and away from contactwith a user.

[0289] Rod 982 may be expelled by any sufficient means such as but notlimited to an explosive propellant for example. It should be noted thatalthough safety mechanism 14 ll′ is depicted as incorporating rod 980and 982, an alternative amount of rods may be incorporated whilereaching similar results. It is also appreciated that amagneto-rheological shock or a biased pivot arm as described inconjunction with safety mechanism 1411 may also be employed to maintainarm 978 in an upward orientation.

[0290] Projectile Stops

[0291] Turning now to FIGS. 65a and 65 b, a safety mechanism 14 mm isshown. Safety mechanism 14 mm includes a projectile stop 1020, forselectively stopping a circular saw blade 1022 in a short period oftime. In this case the angular momentum is transferred to an object thatis not connected to the saw, and thus does not create any unwantedlinear momentum leading to movement.

[0292] In general, projectile stop 1020 includes a firing device 1024for expelling a projectile 1026. In operation, projectile 1026 islaunched into the saw blade 1022 in an opposite direction of rotation ofthe saw blade 1022. When the projectile 1026 contacts the saw blade1022, the kinetic energy and the rotational inertia of the blade 1022are opposing and thus cancel each other. If the energy of the projectile1026 matches the rotational inertia of the saw blade 1022, the blade1022 will be completely stopped.

[0293] Firing device 1024 may comprise any deployment means sufficientto direct projectile 1026 toward blade 1022 with sufficient momentum. Inthis way, firing device may include an explosive device or a mechanicalspring assembly for example. Projectile 1026 may comprise any suitablematerial having a mass sufficient to create adequate momentum upon afiring event to null the angular momentum of blade 1022.

[0294] The operation of projectile stop 1020 will now be described ingreater detail. If a dangerous condition is detected by, for example,one of the sensing mechanisms 12 disclosed herein, firing device 1024 isactivated. Projectile 1026 in turn is fired into the teeth of blade 1022thereby countering the angular momentum of blade 1022 bringing the blade1022 to a stop in a short period of time. Concurrently, power is cutfrom saw 10. An exhausted projectile stop 1020 must be replaced after afiring event with a new projectile stop.

[0295] Engage Blade not Teeth

[0296]FIGS. 66a-66 c show safety mechanism 14 nn having a pin stop 1036,to stop a saw blade 1038 in a very short period of time. Safetymechanism 14 nn is described with respect to a miter saw but it will beappreciated that safety mechanism 14 nn may be employed with other sawsand power tools. Pin stop 1036 is compressed of a channel 1040 that isdisposed around the perimeter of the saw blade 1038 and connected to theframe (not shown) of the saw. Channel 1040 also includes a bore 1042formed through both sides of the channel 1040 for operatively receivingpin stop 1036. If the operator or other system desires to stop the bladein a short period of time, a pin 1044 is driven into the bore 1042 andengages one of a plurality of holes 1046 along the edge of the saw blade1038 to prevent further movement of the blade 1038. Explained further,pin 1044 engages blade 1038 along a outer path 1045 thereof. The blade1038 continues to rotate until pin 1044 falls through an adjacent hole1046. Once pin 1044 is thrust through a hole 1046 (FIG. 66c), blade 1038immediately stops. Alternatively, if a blade not specifically havingholes 1046 arranged around the perimeter of the blade, the pin 1044 maybe driven into the teeth of the blade to stop further rotation of theblade 1038.

[0297] With specific reference to FIGS. 66b and 66 c, the operation ofsafety mechanism 14 nn will be described in greater detail. If adangerous condition is detected by for example one of the safetymechanisms disclosed herein, pin 1044 is rapidly actuated toward sawblade 1038 consequently engaging one of the holes 1046 incorporated insaw blade 1038 thereby immediately stopping the rotation thereof. Pin1044 may be deployed by any sufficient means such as but not limited tobiasing member 1048.

[0298]FIGS. 67a and 67 b illustrate another safety mechanism 14 oohaving a cam stop 1050 to stop a saw blade 1066 in a very short periodof time. Cam stop 1050 is generally composed of a electric module 1052,a fuse 1056 connected to a first end of the electric module 1052, aspacer 1054 connected to the other end of the fuse 1056, a first biasedcam 1058 and second biased cam 1060 retained in a neutral position bythe spacer 1054. In operation, the electric module 1052, upon signalfrom another device (such as a sensing mechanism 12 disclosed herein)releases a high current charge to fuse 1056. Once fuse 1056 is blown,spacer 1054 no longer restrains cams 1058 and 1060. Upon release fromspacer 1054, cams 1058 and 1060 are rotated inward (in a directiondepicted by arrows 1068) by torsional springs 1062 and 1064 to stop sawblade 1066.

[0299]FIGS. 68a and 68 b illustrate a safety mechanism 14 pp includingair bag device 1074 for rapidly moving the hand of the user away fromthe rotating blade 1070. Air bag 1074 is disposed proximate spindle 1080and inner and outerblade clamps 1082, 1084. Air bag 1074 is compressedof a rapidly inflatable vessel 1072 that is positioned adjacent to thesaw blade 1070 and an inflation device 1076 for rapidly inflating theinflatable vessel 1072.

[0300] Inflation device 1076 is preferably configured to inflate vessel1072 with a fluid such as air. Inflation device 1076 may also beconfigured to inflate vessel 1072 with other fluids such as water, gelor the like without departing from the scope of the invention.

[0301] The operation of safety mechanism 14 pp will now be described ingreater detail. If a dangerous condition is detected by for example oneof the sensing mechanisms 12 disclosed herein and it is desirable tomove the hand of the user away from the saw blade, inflation device 1076is operated. Inflation device 1076 rapidly inflates a vessel 1072 thatexpands outward from the tool (from a position diagrammatically depictedin FIG. 68a to a position diagrammatically depicted in FIG. 68b) todrive the hands of the user away from the blade 1070. In this way,vessel 1072 preferably expands to a distance greater than the length ofblade 1070 to inhibit user interface with the teeth of blade 1070.

[0302] It will be appreciated that inflation device 1076 mayalternatively be mounted in other areas adjacent to the saw blade 1070such as for example to a portion of the frame. In this way, inflationdevice 1076 may be arranged to deploy vessel 1072 downward at the handor extremity of the user to bat the same away from contact with the sawblade 1070.

[0303] Referencing now FIG. 69, a safety mechanism 14 qq including fluidbag 1090 is shown. Fluid bag 1090 is composed of at least one inflatablevessel 1092 positioned adjacent to saw blade 1100. Saw blade 1100 isshown disposed on arbor 1102 between inner and outer blade clamps 1104and 1106. Fluid bag 1090 contains magneto-rheological fluid. Once thesaw blade 1100 is desired to be stopped, a current is applied to themagneto-rheological fluid, the inflatable vessel 1092 inflates andcontacts the saw blade 1100. Consequently, the friction generatedbetween fluid bag 1090 and saw blade 1100 causes the saw blade torapidly slow to a complete stop.

[0304] Not Engaging Blade

[0305]FIG. 70 shows a safety mechanism 14 rr. Safety mechanism 14 rrincludes a jam stop 1116, to stop a saw blade 1118 in a very shortperiod of time. Jam stop 1116 is composed of a first gear 1120 mountedto the rotating arbor (not specifically shown) and a second gear 1122drivingly connected to the first gear 1120 and a wedge 1124. The firstgear 1120 and second gear 1122, rotate in opposite directions to oneanother, due to the meshing of the gears.

[0306] If a dangerous condition is detected by, for example one of thesafety mechanisms 12 disclosed herein, biasing member 1126 drives wedge1124 in a direction depicted by arrow 1130 between the intermeshing gearteeth of the first gear 1120 and the gear teeth of the second gear 1122.Wedge 1124 efficiently stops the rotation of saw blade 1118 byprecluding subsequent rotation of first and second 1120 and 1122. Tip1132 of wedge 1124 is comprised of a rigid material suitable toeffectively dissipate the rotational energy and momentum of saw blade1118.

[0307] It will be appreciated that jam stop 1116 may comprisealternative configurations within the scope of the present invention.For example, a hub may be mounted to gear 1120 or 1122. In this regard,wedge 1124 may be configured to engage a hub extending from gear 1120 or1122. The hub may also include protrusions extending around acircumference thereof. In this configuration, wedge 1124 is preferablycomprised of a pliable material such as plastic allowing for theprotrusions of the hub to dig into wedge 1124 in a stop event. Explainedfurther, in a stop event, wedge 1124 is actuated into the hub causingprotrusions to dig into the wedge 1124 until the hub stops rotating. Inthis manner, the gear having the hub disposed thereon stops rotatingconsequently stopping rotation of blade 1118.

[0308] Brake-Away Features for Braking Configurations

[0309] According to many of the safety mechanisms 14 employed herein,the safety mechanisms 14 are configured to rapidly stop a saw blade fromrotating. In this manner, abruptly stopping a saw blade from rotatingmay cause damage to the motor of the saw 10 or other internal gearingsuch as the spindle for example. The following drive system protectionmechanisms 16 are employed to limit the force a saw blade motor andrelated drive system must endure during a rapid stopping event. Ingeneral, the protection mechanisms 16 may be used concurrently with anysensing mechanism 12 or safety mechanism 14 disclosed herein. Protectionmechanisms 16 include break away features which allow the saw blade tostop rapidly (upon actuation of a safety mechanism for example), whileallowing the drive system to continue rotating.

[0310] Referencing FIG. 71, a protection mechanism 16 a is shownoperatively associated with a miter saw 100 a. Again, while protectionmechanism 16 a is shown associated with a miter saw, it will beappreciated that protection mechanism 16 a may be employed with otherpower tools within the scope of this invention. Drive system 1156 ofmiter saw 10 a includes a motor 1140 operatively coupled for rotationwith a blade arbor shaft 1142. Blade 1144 is fixed for rotation betweeninner and outer blade clamps 1146 and 1148 respectively. Inner bladeclamp 1146 includes a key 1150 extending into complimentary bores 1152within spindle 1142. In this way, blade clamps 1146 and 1148, in turn,couple blade 1144 for rotation with spindle 1142.

[0311] During a stopping event, such as by implementation of one of thesafety mechanisms 14 disclosed herein, blade 1144 is rapidly stopped.Concurrently, key 1150 shears from inner blade clamp 1146 therebyallowing the drive system 1156 including spindle 1142 and motor 1140 tocontinue rotating. As a secondary measure, the power may be cut to thesaw 100 a after a stopping event allowing the drive system 1156 toslowly spin to a complete stop. Nonetheless, in either scenario, innerand outer blade clamp 1146, 1148 together with blade 1144 remain stoppedas drive system 1156 continues to operate or slowly comes to a stop.

[0312] After a stop event, the existing inner blade clamp 1146 isdiscarded and a new inner blade clamp having an integral key 1150 isemployed. Key 1150 is preferably made of a material, such as but notlimited to aluminum for example, having sufficient rigidity to maintainthe blade clamp in a coupled relationship with the spindle 1142 duringoperation while also having characteristics allowing the key 1150 to besheared from the blade clamp 1146 during a stopping event. It isappreciated that key 1150 may also include other details allowing for aselectively fixed relationship between the blade clamp 1146 and spindle1142. In addition, it will be appreciated that outer blade clamp 1148may alternatively be keyed to spindle 1142 yielding similar results.Moreover, while protection system 16 is described as cooperating with asafety mechanism 14 that negotiates the saw blade 1144 to stop the same,protection system 16 may also be employed to a safety system 14 which isalternatively configured to manipulate the saw clamp.

[0313] Turning now to FIG. 72, an alternative protection mechanism 16 bis shown incorporated with power tool 100 b. Like reference numeralswill be used to designate like components of protection mechanism 16 a.Inner blade clamp 1166 is keyed to outer blade clamp 1168 by feature1170. Feature 1170 may include threaded fasteners such as screws oralternatively pins. In this way, feature 1170 is configured to shearupon a stopping event such that inner and outer blade clamp 1166, 1168may rotate or stop independently of each other. Feature 1170 mayalternatively be an adhesive bond capable of separating inner and outerblade clamp 1166, 1168 upon a stopping event. A blade bolt 1172 clampsinner blade clamp 1166 to the spindle 1142.

[0314] During a stopping event, blade 1176 is rapidly stopped by forexample one of the safety mechanisms 14 disclosed herein. Rapid stoppingof blade 1176 causes feature 1170 to shear thereby uncoupling the innerblade clamp 1166 from the blade 1176 and outer blade clamp 1168. In thisregard, drive assembly 1156 including spindle 1142 and motor 1140 arefree to continue rotation while blade 1176 is stopped minimizing injuryto the operator and the power tool 100 b. Lip 1180 extends from bladebolt 1172 outwardly beyond the inner diameter of outer blade clamp 1168.During a stop event, outer blade clamp 1168 and blade 1176 may have atendency to travel toward blade bolt 1172. Lip 1180 retains outer bladeclamp 1168 between blade bolt 1172 and inner blade clamp 1166 precludingthe outer blade clamp 1168 and blade 1176 from falling off the spindle1142.

[0315] In an additional embodiment, biasing members may be employedbetween inner blade clamp 1166 and blade 1176 for further urging blade1176 and outer blade clamp 1168 away from inner blade clamp 1166.

[0316] Miscellaneous Braking

[0317] Referencing FIG. 73 safety mechanism 14 ss having a secondary hub1180 is shown operatively associated with miter saw 10 ss. Secondary hub1180 is coupled for rotation with spindle 1188 and is disposed adjacentinner blade clamp 1182. Blade 1186 is mounted for rotation between innerand outer blade clamp 1182 and 1184. Protrusions 1190 extend radiallyfrom secondary hub 1180. As will be described in greater detail,stopping device 1192 is disposed adjacent hub 1180 and is arranged tolinearly engage protrusions 1190 of hub 1180 during a stopping event.

[0318] If a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein, stopping device 1192 is actuatedinto protrusions 1190 extending from hub 1180. Stopping device 1192 maybe actuated by a firing device or a mechanical actuator for example.Further, stopping device 1192 is preferably comprised of a pliablematerial such as plastic sufficient to dig into protrusions 1190 duringa stopping event. Hub 1180 and stopper 1192 must be replaced after astopping event.

[0319] It will be appreciated that stopper 1192 may alternatively beconfigured to engage inner blade clamp 1182 directly. In this way, innerblade clamp 1182 may have a friction surface disposed on an outercircumference thereof for stopper 1192 to engage. Additionally, safetymechanism 14 ss may also include a friction or keyed mating surfacebetween the inner blade clamp 1182 and blade 1186 to further encourageblade 1186 to stop with inner blade clamp 1182 during a stop event.

[0320] Miscellaneous Stop

[0321] Turning now to FIGS. 74a and 74 b, a safety mechanism 14 ttemploying nautilus stop 1196 is shown. Nautilus stop 1196 includes aninvolute spline shaped cam member 1198 disposed adjacent a saw blade1200. A biasing member 1206 biases cam 1198 into the positiondiagrammatically depicted in FIG. 74b. In this regard, cam 1198 isretained or otherwise maintained in the position shown in FIG. 74a by alatch 1208 during normal operation of the tool. During a stop event, aswill be described in greater detail, cam 1198 rotates about axis 1202 ina counterclockwise direction from the position as diagrammaticallydepicted in FIG. 74a to the position diagrammatically depicted in FIG.74b. Cam 1198 is made of a strong material sufficient to absorb therotational energy from blade 1200. Similarly, the material of cam 1198must be sufficiently rigid to bring blade 1200 to a complete stop.Surface 1204 of cam 1198 is shown having a smooth radial contour,however, surface 1204 may alternatively have an irregular surface toencourage adequate gripping action between the cam 1198 and blade 1200.

[0322] The operation of safety mechanism 14 tt will now be described. Ifa dangerous condition is detected by for example one of the sensingmechanisms 12 disclosed herein, latch 1208 releases cam 1198 from theposition shown in FIG. 74a. As such, biasing member 1206 urges cam 1198in a counterclockwise direction toward rotating saw blade 1200. Uponcontact, the rotational energy of the blade 1200 (rotating in aclockwise direction) will encourage cam 1198 to further rotatecounterclockwise progressively increasing engagement and deceleration ofblade 1200. It will be understood that cam 1198 may comprise othergeometries without departing from the scope of this invention.Additionally, it is appreciated that additional cams 1198 may beconcurrently employed around the periphery of saw blade 1200.

[0323] Turning now to FIGS. 75a and 75 b, a safety mechanism 14 uuincluding cam actuated brake 1220 is shown. An eccentric cam 1222 isfixed for rotation with blade 1224. Cam actuated brake 1220 includes acam follower 1226 positioned adjacent the cam 1222 and near the smallestradius (as shown in FIG. 75a). Cam follower 1226 is disposed in anaxially displaced position with respect to cam 1222 during normaloperation of the tool. A brake arm 1230 is coupled to cam follower 1226and extends in a direction generally tangential from blade 1224.

[0324] The operation of safety mechanism 14 uu will now be described ingreater detail. If a dangerous condition is detected by for example oneof the sensing mechanisms 12 disclosed herein, cam follower 1226 isdisplaced axially toward blade 1224 whereby cam 1222 and cam follower1226 are engaged. Axial displacement of cam follower 1226 may beachieved by any sufficient means such as a mechanical actuator orexplosive firing event for example. Accordingly, clockwise rotation ofcam 1222 will urge cam follower from a position diagrammaticallydepicted in FIG. 75a to a position diagrammatically depicted in FIG.75b. As shown, brake arm 1230 is displaced into saw blade 1224 causingthe teeth of saw blade 1224 to dig into arm 1230 until blade 1224 comesto an immediate stop.

[0325] It will be appreciated that cam 1222, cam follower 1226 and brake1230 may comprise alternate geometries without departing from the scopeof the present invention. Furthermore, cam follower 1226 and brake 1230may alternatively be configured to engage another rotating element ofthe saw such as the arbor shaft or blade clamp for example.

[0326] Referencing now FIGS. 76a and 76 b, safety mechanism 14 wincluding brake pawls 1232 is shown. Brake pawls 1232 are disposedadjacent saw blade 1234 in a diametrically opposed relationship. Brakepawls 1232 are pivotally coupled to a portion of the saw (notspecifically shown) at pivot joints 1236. During a stopping event pawls1232 are pivotally displaced about pivot joints 1236 toward blade 1234.

[0327] The operation of safety mechanism 14 w will now be described ingreater detail. If a dangerous condition is detected by for example oneof the safety mechanisms 12 disclosed herein, brake paws 1232 are thrustinto blade 1234 from a position diagrammatically depicted in FIG. 76a toa position diagrammatically depicted in FIG. 76b. Preferably, pawls 1232are rotated in a direction opposing rotation of blade 1234. In this way,pawls 1232 rotate counterclockwise into engagement with a clockwiserotating blade 1234. Brake paws 1232 may be urged into engagement withblade 1234 by for example biasing members, mechanical actuators orexplosive device for example.

[0328] Safety Blade

[0329] Referencing FIGS. 77a and 77 b, safety mechanism 14 ww is shown.Safety mechanism 14 ww includes radially actuable guard sections 1250disposed on saw blade 1252. Guard sections 1250 are configured torapidly displace outwardly beyond the perimeter of blade 1252 during astop event. Guard sections 1250 preferably are retained in a position asshown in FIG. 77a by a latch or similar retaining device (notspecifically shown) during normal operation.

[0330] If a dangerous condition is detected by for example one of thesensing mechanisms 12 disclosed herein, guard sections 1250 are urgedoutwardly from a position as shown in FIG. 77a to a position as shown inFIG. 77b. Guard sections may be urged by any suitable means such as butnot limited to mechanical biasing members or an explosive device. Guardsections are preferably comprised of a durable pliable materialsufficient to displace a finger or a hand of a user away from the sawblade 1252.

[0331] It will be appreciated that alternative configurations of guardsections 1250 may be employed. For example an alternate amount of guardsections 1250 may be used or alternate geometries may be used for guardsections 1250.

[0332] External Forces Braking

[0333] Another consideration in preventing injury as a result of contactwith the rotating blade of a saw is the size and configuration of thesaw blade that is being used. In many applications a standard blade isused to make cuts through an entire piece of wood. However, additionaltypes of circular saw blades are available to perform numerous otherremoval functions such as dado operations. These blades and conventionalblades are often made in varying sizes, which may not function correctlywith presently installed stop devices. Therefore, the present inventionprovides a device that allows a user to position a saw brake mechanismin a desired position depending on the size of the saw blade being used.

[0334]FIGS. 78a-78 c show a safety mechanism 14 xx employing brakemodule 1270. Brake module 1270 extends from arbor bracket 1272 andincludes actuation fork 1274 attached thereto. Arbor bracket 1272rotatably couples saw blade 1276 at shaft 1278. Brake module 1270 whichis connected to arbor bracket 1272 through a pin 1282 in a slot 1286,engages the periphery of blade 1276 to rapidly slow it down during astop event. If a large blade is used (referred to as 1276′ in FIG. 78c),the pin 1282 in the slot 1286 is actuated by the actuation fork 1274 tothe end of slot 1286 that is further away from the blade 1276 (FIG.78c). If a smaller blade is going to be used (referred to as 1276 inFIG. 78b) the pin 1282 in the slot 1286 is actuated by the actuationfork 1274 to the end of slot 1286 that is nearest to the blade 1276(FIG. 78b).

[0335] During a stopping event, brake module 1270 is rotated by suitablemeans toward rotating saw blade 1276. In this way, arbor bracket 1272may pivot about shaft 1278 clockwise as viewed from FIG. 78b.Alternatively, brake module 1270 may rotate about shaft 1282 in acounterclockwise direction toward rotating saw blade 1276 as viewed fromFIG. 78b.

[0336] While the following description is provided with reference to atable saw, it is readily understood that the contact detection system ofthe present invention is applicable to a variety of power tools and/orwoodworking tools, including (but not limited to) miter saws, radial armsaws, circular saws, band saws, joiners, planars, nailers, drills, etc.

[0337] Woodworking power tools of the type described herein aretypically powered by an electrical power system for connection to acommonly available electrical connection. Therefore the safety devicesof the present invention are illustrated for use with power tools havinga power source that utilizes electrical energy. However, it iscontemplated that the woodworking power tools utilizing a differentpower source may also employ the safety systems described herein and notdepart from the scope of the present invention.

[0338]FIG. 79 illustrates a safety mechanism 14 yy for use with a tablesaw 10 yy, box guard 1300. Box guard 1300 is generally compressed of ariving knife 1302 that is substantially similar in width to saw blade1304. Riving knife 1302 is oriented coplanar with saw blade 1304 andpositioned directly behind slot 1306. Riving knife 1302 preferablyextends perpendicularly upward with respect to planar top surface 1308to a height that is generally above saw blade 1304. Attached to the topof riving knife 1302 is a plate 1310. Plate 1310 is substantiallyrectangular in shape, having a width that is substantially wider thansaw blade 1304 and a length that extends over the top portion of sawblade 1304. Plate 1310 is connected to a box 1312, which covers sawblade 1304.

[0339] In a preferred embodiment, box 1312 is constructed in a box shapehaving two adjacent sides removed. The first removed side is positionedadjacent to the planar top surface 1308 to allow saw blade 1304 to behoused therein. The second removed side is positioned adjacent to theback of saw blade 1304, near plate 1310 and riving knife 1302. Box 1312is attached to plate 1310 by removable fasteners such as, bolts or pullpins, to form a hinge mechanism that allows box 1312 to be selectivelyraised to allow access to saw blade 1304. Box 1312 may include a rampshaped guide portion 1318 formed on the front edge of the box 1312 toactuate box 1312 when in contact with a piece of material.Alternatively, a knob 1320 or actuator may be utilized to actuate box1312 to an open position. Additionally, a set of louvers 1324 isprovided to allow monitoring of the blade 1304 while limiting the sizeand number of objects that may contact saw blade 1304.

[0340]FIG. 80 shows safety mechanism 14 zz according to anotherembodiment of the present invention. Safety mechanism 14 zz includesguard plate assembly 1350 including a riving knife 1352 mounted to tablesaw 10 zz as known in the art for guiding a workpiece. Releasablyattached to the distal end of riving knife 1352 is a guard plate 1354that extends over saw blade 1386 to operatively prevent inadvertentcontact with saw blade 1386. As shown guard plate 1354 includes a groove1356 extending along the rear portion of guard plate 1354 to receive thetop edge of riving knife 1352. Extending over groove 1356 is a yoke 1360that retains the front end of riving knife 1352. Located at the rear ofguard plate 1354 is manually rotatable latch 1362 to releasably attachguard plate 1354 to the rear end of riving knife 1352. If the use ofguard plate 1354 is desired, the front end of riving knife 1352 isinserted into yoke 1360 and latch 1362 is actuated to engage the rearportion of riving knife 1352. In this configuration, guard plate 1354provides a protective member that extends over the length of saw blade1386. If the use of guard plate 1354 is not desired, guard plate 1354may be removed by rotating latch 1362 to a disengaged position andsliding guard plate 1354 forward so that yoke 1360 is not in contactwith the leading edge of riving knife 1352.

[0341] As shown in FIG. 81, a safety mechanism 14 ba is shown to includea sight guard 1380. Like components of safety mechanism 14 zz are usedto designate like components of safety mechanism 14 ba. Sight guard 1380is generally composed of a rectangular translating guard 1382 having aplurality of louvers 1384 disposed therethrough for observing the sawblade 1356. Translating guard 1382 extends through a simple slot 1390 inguard frame 1392 substantially similar in size to translating guard1382. Sight guard 1380 is selectively positioned in an infinite numberof positions ranging from fully closed, wherein the leading end oftranslating guard 1382 is adjacent to planar top surface 1394, to fullyopen, wherein the leading end of translating guard 1382 is adjacent toguard frame 1392. In operation, translating guard 1382 is actuatedupward until the leading end is above the top surface of a workpiece(not shown). As the workpiece is moved toward the blade 1396, theleading edge of translating guard 1382 follows along the top surface ofthe workpiece. In this configuration, sight guard 1380 allows the userto view the interaction between the saw blade 1396 and the workpiecewhile prevented from contacting saw blade 1396.

[0342]FIG. 82 shows safety mechanism 14 ba′ incorporating a pluralityrolling members 1410 that follow along the inner and outer surface ofguard 1380 to promote smooth translation of guard 1380. Like referencenumbers of safety mechanism 14 ba are used to designate like componentsof safety mechanism 14 ba′. In this regard, the operation of safetymechanism 14 ba′ is substantially similar to safety mechanism 14 ba.

[0343]FIG. 83 shows safety mechanism 14 bb having sensing guard assembly1420. Sensing guard assembly 1420 is generally comprised of a rivingknife 1422 and a top plate 1424 mounted to a table saw as known in theart. A sight guard 1430 is rotatably attached to the front end of thetop plate 1424, a sensing device 1432 is attached to the front end ofsight guard 1430 and an actuation mechanism 1436 including motor orsolenoid 1434 for selectively actuating the sight guard 1430. Sightguard 1430 is preferably formed to have a plurality of louvers 1440 toallow the user to inspect the interaction between the saw blade 1444 andthe workpiece while precluding user interface with the saw blade 1444.Connected to the front of sight guard 1430 is sensor device 1432oriented to detect in the downward direction. If sensor device 1432detects a workpiece, it sends a signal to an actuation mechanism 1436 toopen sight guard 1430. Actuation mechanism 1436 opens sight guard 1430to allow a workpiece to access saw blade 1444. The downward orientationof sensor device 1432 prevents objects such as an operator's finger fromcontacting saw blade 1444 because the blade 1444 must be actuated upwardby the person to allow for entrance with the blade 1444. Therefore, theoperator would know that they were approaching the saw blade 1444.Alternatively, a sensing device that detects the difference betweenhuman tissue and a workpiece as is discussed herein may be installed tofurther prevent inadvertent contact with the saw blade 1444.

[0344] As shown in FIG. 84 a safety mechanism 14 bc including a rivingknife assembly 1450 is shown. In operation of a table saw, it may bedesired to utilize a riving knife 1452 to guide a workpiece whileperforming groove, finger joint, rabbit, or cheek cuts. However, rivingknives are not able to be used to many other types of cuts. Safetymechanism 14 bc allows for easy installation when using riving knife1452 and easy removal when not using riving knife 1452. In a preferredembodiment, riving knife assembly 1450 includes a base member 1456having a slot 1460 therein oriented coplanar and behind a saw blade (notspecifically shown). Base member 1456 includes a pull pin 1464 mountedalong an elongated side for selectively engaging a riving knife 1452having a retention hole 1466 formed complementary to pull pin 1464.

[0345] If the use of riving knife 1452 is desired, the operator mayslide the riving knife 1425 into the base member 1456 and actuate pullpin 1464 away from base member 1456 to install riving knife 1452. Onceriving knife 1452 is fully seated, the operator may return pull pin 1464to the original position to lock riving knife 1452 to base member 1456.If the use of riving knife 1452 is not desired, the operator actuatespull pin 1464 away from base member 1456 to extract riving knife 1452from base member 1456.

[0346] With reference to FIG. 85, a safety mechanism 14 bd includingguard retainer 1480 is shown. Guard retainer 1480 is configured to lockthe blade guard 1450 to pivot plate 1452 and thus allow access to arborbolt 1454. A screw 1460 maintains the guard and pivot plate 1452 in theposition shown. During operation, lower guard 1450 is rotated upward ina counterclockwise direction. Screw 1460 is loosened to clear tab 1462on pivot plate 1452. Concurrently, retainer 1466 biases guard 1450counterclockwise thereby holding the guard 1450 in a retained position.Guard 1450 and pivot plate 1452 are further rotated together until pivotplate tab 1462 moves beyond screw 1460. Screw head 1460 then precludesblade guard 1450 and pivot plate 1452 from rotating clockwise. In thisway, the user may gain unimpeded access to arbor bolt 1454 during ablade change.

[0347] Turning now to FIG. 86, a safety mechanism 14 be includingmagneto-rheological damper 1470 is shown operatively associated with amiter saw 10 be. Safety mechanism 14 be is preferably used inconjunction with another safety mechanism 14 disclosed herein. If asensing mechanism 12 initiates a stop event by using a braking forcesuch as those described in association with other safety mechanisms 12.During a stopping event, the rapid deceleration will tend to cause theblade 1472 and arm 1474 to travel downward in the direction of workpiece1478 and also toward potential additional contact with a user. Tocounter this, magneto-rheological damper 1470 precludes downward travelof blade 1472 and arm 1474. As is well known, a magneto-rheologicalfluid damper utilizes a fluid which can have the viscosity alteredthrough the application of a magnetic field. During a stop event, asignal is preferably sent to damper 1470 at the same time a sensingmechanism 12 senses a dangerous condition.

[0348]FIGS. 87 and 88 show a safety mechanism 14 bf for use with a powertable saw 10 bf including blade retraction system 1500. Blade retractionsystem 1500 is designed to retract a saw blade 1502 under the tableportion 1504 of a table saw 10 bf to prevent or reduce injurious contactbetween the saw blade 1502 and an operator of the table saw 10 bf.Again, although the present invention is shown in combination with apower table saw 10 bf, it is appreciated that the teachings of thepresent invention may be applied to other types of power saws having arotating saw blade, such as a miter saw, chop saw, or circular saw.

[0349] The blade retraction system 1500 is comprised of an arbor bracket1508 supporting the saw blade 1502 and coupled to a portion of the tablesaw 10 bf, a sector gear 1510 adapted to travel along a portion of thearbor bracket 1508, a clutch mechanism 1514 slidably coupling the sectorgear 1510 to the arbor bracket 1508, a worm gear 1520 operable to adjustthe position of the sector gear 1510 and an actuating device 1526coupled to the sector gear 1510 and the arbor bracket operable totranslate the arbor bracket 1508 relative to the sector gear 1510 toretract the saw blade 1502 beneath the table portion 1504 of the tablesaw 1504 to prevent injurious contact between the saw blade 1502 and theoperator of the table saw 10 bf.

[0350] The arbor bracket 1508 of the present invention is shown to becomprised of a support arm 1529 and an adjustment arm 1530 defined by abore 1532. The support arm 1526 of the arbor bracket 1508 extendsgenerally horizontal and includes a bore adapted to receive a spindle1536. The spindle 1536 is adapted to be coupled to the saw blade 1502and allow rotation of the saw blade 1502 relative to the arbor bracket1508. The spindle 1536 also engages a belt or other device (not shown)that drivingly engages the saw blade 1502 to operatively rotate the sawblade 1502. The adjustment arm 1530 of the arbor bracket 1508 generallyinclude an arc shaped surface 1540 that is substantially concentric withthe bore 1532. The bore 1532 is adapted to engage a pivot pin 1542 thatis coupled to a portion of the table saw 10 bf to allow arbor bracket1508 to rotate relative to the table saw 10 bf.

[0351] The sector gear 1510 is formed to have a generally arcuate shapehaving a first surface 1552 substantially conforming to the arc shapedsurface 1540 of the arbor bracket 1508 and a gearing portion 1554 alsoformed in an arcuate shape substantially concentric to the bore 1532 andhaving a plurality of gear teeth 1560. The sector gear 1510 is locatedto allow the first side of the sector gear 1510 to be adjacent to thearc shaped surface 1540 of the arbor bracket 1508 to allow relativetranslation therebetween.

[0352] The clutch mechanism 1514 is designed to couple the arbor bracket1508 to the sector gear 1510, but allow relative translationtherebetween when a requisite force is applied to either the arborbracket 1508 or the sector gear 1510. The clutch mechanism 1514 is shownto include a biased detent mechanism 1566 extending from the arborbracket 1508 and engaging the sector gear 1510. The detent mechanism1566 is comprised of a detent member 1568 that is biased toward thesector gear 1510 by a biasing member 1570. The detent member 1568engages the first surface 1572 of the sector gear 1510 to preventtranslation between the sector gear 1510 and the arbor bracket 1508. Itis contemplated that the other type of clutch mechanisms 1514, may beused to couple the arbor bracket 1508 to the sector gear 1510.Additionally, it is appreciated that the clutch mechanism 1514 may beattached to various locations on the sector gear 1510.

[0353] The worm gear 1520 is adapted to engage the sector gear 1510 tocontrol movement of the sector gear 1510. The worm gear 1520 isgenerally comprised of a shaft member 1580 and a threaded gear portion1852. The worm gear 1520 may to be rotated in one of a number of wayssuch as electric actuator or crank. The threaded gear portion 1582 ofthe worm gear 1520 is adapted to engage some of the plurality of teeth1560 of the sector gear 1520. As the worm gear 1520 is rotated, thethreaded gear portion 1582 meshes with the gear teeth 1560, therebycause the arbor bracket 1508 and attached components to rotate clockwiseor counterclockwise depending on the direction of rotation of the wormgear 1520. In operation, the worm gear 1520 is utilized to control theheight of the saw blade 1502 relative to the top of the table portion1504 of the table saw 10 bf.

[0354] In a first embodiment, the actuating device 1526 is shown to berotatably coupled to the sector gear 1510 and the arbor bracket 1508.The actuating device 1526 is comprised of a piston 1584 and a cylinder1586. The piston 1586 is coupled to one of the sector gear 1510 and thearbor bracket 1508. The cylinder 1586 is coupled to the other of thesector gear 1510 and the arbor bracket 1508. The actuating device 1526also includes a propellant material disposed in the cylinder 1586 andoperable to expand upon the activation of a triggering device (notshown). Upon activation of the triggering device (not shown), the piston1586 portion of the actuating device 1526 expands axially outwardincreasing the length of the actuating device 1526. The propellantmaterial is preferably an electrically activated explosive material.However, it is contemplated that other types of propellant materials maybe utilized in the present invention. It is also contemplated that amechanical device may be utilized in the place of actuating device 1526.

[0355] In operation, the triggering device (not shown) is activatedcausing the actuating device 1526 to expand axially. As the actuatingdevice 1526 expands, the arbor bracket 1508 and the sector gear 1510 aredriven apart. As the actuating device 1526 expands, the arbor bracket1508 is driven in a counterclockwise direction. As the arbor bracket1508 rotates, the support arm 1526 and the saw blade 1502 are rotateddownward to a position under the table portion 1504 of the table saw 10bf. Once the saw blade 1502 is beneath the table portion 1504 of thetable saw 10 bf, the possibility of contact between the saw blade 1502and the operator is eliminated.

[0356] As shown in FIG. 88, a bumper pad 1590 may be incorporated intothe blade retraction system 1500 of safety mechanism 14 bf of thepresent invention. It is appreciated that like reference numbers will beused to designate like components. The bumper pad 1590 is positionedrearward of the arbor bracket 1508 and is adapted to receive the rearend of the arbor bracket 1508 after activation of the actuating device1526. The bumper pad 1590 dissipates the energy of the impacting arborbracket 1508. The bumper pad 1590 is shown to be formed of a permanentlydeforming material such as a yielding plastic, a crushing foam or adeformable honeycomb structure. It is also contemplated that the bumperpad 1590 may be constructed of a dampening material such as anengineering foam, or a high friction engagement material such aselastomers.

[0357]FIG. 89 illustrates a safety mechanism 14 bg employing analternate actuation mechanism 1526′. The basic structure of the bladeretraction system 1500″ is substantially similar to the previousembodiment described above. However, the actuating device 1526′ isdifferent. The actuating device 1526′ includes a cylinder 1592 that isintegrally formed in the arbor bracket 1508. A piston 1594 is adapted toengage the integral cylinder 1592. A first end 1596 of the piston 1594is formed in a frustum spherical shape to allow the piston 1594 tomaintain engagement with the inner walls of the cylinder 1592. The otherend of the piston 1594 is rotatably coupled to the sector gear 1510.Additionally, it is contemplated that a piston having a compliantsealing cap engaging the inner walls of the cylinder may be used. Thepiston/cylinder arrangement operates substantially similar to thepropellant actuated device 1526 described above. It is also contemplatedthat a mechanical device may be utilized in the place of actuatingdevice 1526′.

[0358]FIG. 90 illustrates safety mechanism 14 bh. In this embodiment, anactuation device 1526″ is coupled to the arbor bracket 1529′ and aportion of the frame of the table saw 10 bh. The actuation device iscomprised of a piston 1608 and cylinder 1610 substantially similar tothe piston/cylinder arrangement of the actuation device 1526′. Thealternate positioning of the piston 1608 and cylinder 1610 arrangementoperates in substantially similar to the actuation device disclosedabove.

[0359] Referring to FIG. 91, a safety mechanism 14 bi for a power tool10 bi having a circularly rotating blade 1650 is shown diagrammatically.The power tool 10 bi is generally comprised of an arm 1652 rotatablycoupled to a rigid base 1654 and having a power saw 1656 attached to thedistal end of the arm 1652. The safety mechanism 14 bi includes abraking device 1660 coupled to the base 1654 and to the arm 1652operable to engage the saw blade 1650 of the power saw 1656. The safetymechanism 14 bi of the present invention is shown for use with a mitersaw. It is contemplated that the present invention may be utilized withother types of power tools having a circular blade. For example, thesafety mechanism 14 bi of the present invention may be adapted for usewith a radial arm saw, a table saw or a chop saw.

[0360] The base member 1654 of tool may be formed as an “L”-shapedmember having a first and a second portions 1662 and 1664 that aresubstantially perpendicular. The outwardly extending first portion 1662generally supports the safety mechanism 14 bi and includes a firstconnection 1670 to rotatably couple a portion of the braking device 1660to the base member 1654 to provide proper operation of the brakingdevice 1660. The upwardly extending second portion 1664 includes asecond connection 1672 to rotatably couple an end of the arm 1652 to thebase member 1654 to allow articulation of the power saw 10 bi coupled tothe other end of the arm 1652. However, it is understood that the basemember 1654 may be constructed in a variety of different configurationsthat allow for proper function of the arm 1652 and the braking device1660.

[0361] The arm 1652 of the safety mechanism 14 bi is generally formed inan “L”-shape having a first extending end 1676 and a second extendingend 1678. The first extending end 1676 is rotatably coupled to the basemember 1654 and the second upwardly extending end 1678 is adapted tolocate the power saw 1656 and specifically the axis of rotation 1680above the first extending end 1676. The arm 1652 also includes a brakeconnection 1682 for coupling a brake device thereto. The brakeconnection 1682 is located proximate to the saw blade 1650 of the powertool 10 bi. The arm 1652 is designed to allow proper articulation of thesaw blade 1650 with respect to a workpiece (not shown). The arm 1652 isshown to be formed of a rigid material having a relatively high strengthsuch as steel. However, it is contemplated that the arm 1652 may beconstructed of other material having suitable properties.

[0362] The power saw 1656 is attached to the distal end of the arm 1652.The arm 1652 allows the power saw 1656 to be articulated along a pathdefined by the distal end of the arm 1652. The power saw 1656operatively rotates the saw blade 1650 in the clockwise directionindicated by arrow 1688.

[0363] The power saw 1656 portion of the present invention is shown tobe constructed of a AC electric motor coupled to a saw blade 1650 by anarbor. However it is contemplated that many different varieties of powersaws, such as DC electric and saws having a hydrocarbon based engine,may be used with the safety mechanism 14 bi of the present invention.

[0364] The braking device 1660 includes a brake 1690, coupled to the arm1652 and operable to engage the saw blade 1650 upon translation of anactivation mechanism 1692. The activation mechanism 1692 is operable tobe activated on the occurrence of a predetermined event, such as asignaling by the operator, jammed workpiece, or detection of a dangerouscondition by a sensing mechanism 12 as disclosed herein.

[0365] The activation mechanism 1692 is generally comprised of a piston1696 coupled to the brake connection 1682 of the arm 1652 and a cylinder1698 having an explosive material 1700 disposed therein and coupled tothe base 1654. The explosive material 1700 disposed in the cylinder 1698may be activated in any number of ways known to activate explosives 1700such as temperature or spark.

[0366] In a first preferred embodiment the brake 1690 is formed to havea link 1706 rotatably coupled to the arm 1652. The link is generallycomprised of a connection arm 1710 and a push arm 1712. The connectionarm 1710 is rotatably coupled to the distal end of the piston 1696. Thepush arm 1712 is located proximate to the edge of the saw blade 1650 andincludes a brake pad 1718 adapted to engage the saw blade 1650.

[0367] Upon activation of the activation portion, the connection arm1710 of the link 1706 is driven upward rapidly from the force of theexplosives 1700. The use of explosives 1700 is preferred over many othercommonly known biasing devices because explosives 1700 provide a largeforce very rapidly. This large and rapid force allows the saw blade 1650of the power saw 10 bi to be stopped in a short period of time, therebyreducing the chance of serious injury from contact with the saw blade1650. As the connection arm 1710 of the link 1706 is driven upward, thepad 1718 located on the push end of the link 1706 is driven intoengagement with the edge of the saw blade 1650. The saw blade 1650 israpidly slowed as the teeth of the saw blade 1650 engage the pad 1718until the saw blade 1650 is stopped.

[0368] Additionally, the relative location of the pad 1718, above theaxis of rotation 1680 of the saw blade 1650 causes the rotationalinertia of the saw blade 1650 to be dissipated in the upward direction,thus moving the saw blade 1650 and power saw 1656 away from theoperator.

[0369] A second embodiment of a brake is shown in FIG. 93. The brake1720 is similar to the brake 1690, and thus only portions of brake 1720that are different will be discussed. The push arm 1722 of link 1706 isadapted to engage a first and a second pivoting break members 1728 and1730. The brake members 1734 and 1736 are adapted to engage the edge ofthe saw blade 1650. The first and the second brake members 1728 and 1730include a first and second cam surfaces 1740 and 1742 that engage afirst and second edges 1744 and 1746 of the push arm 1722. As the firstand second brake members 1734 and 1736 are activated to a first andsecond brake pads 1734 and 1736 engage the edge of the saw blade 1650.

[0370] A third embodiment of a brake is shown in FIG. 94. The brake 1750includes a wedge or panel brake 1752 adapted to engage the saw blade1650. Upon activation of the brake 1750, push arm 1722 forces wedge 1752into blade 1650. As wedge 1752 engages the saw blade 1650, the wedge1752 engages the teeth of blade 1650. The wedge shape of wedge 1752causes it to be drawn into further engagement with the saw blade 1650,until the saw blade 1650 is stopped.

[0371] While the invention has been described in its presently preferredform, it will be understood that the invention is capable ofmodification without departing from the spirit of the invention as setforth in the appended claims.

What is claimed is:
 1. A method for detecting the position of a safetyguard relative to an active portion of a woodworking machine comprising:establishing a predetermined safe operating position of the safetyguard; positioning a first electrical contact on the safety guard;positioning a second electrical contact on a portion of the woodworkingmachine; transmitting an electrical signal from said first electricalcontact, said second electrical contact receiving said electrical signalonly when the safety guard is in said safe operating position; andactivating a protective operation when said signal is not received bysaid second electrical contact.
 2. The method of claim 1 wherein thestep of establishing a predetermined safe operating position furthercomprises coupling the safety guard to the woodworking machine, therebyforming a closed circuit between said first electrical contact, saidsecond electrical contact and a power switch for the woodworkingmachine.
 3. A power tool having a sensing mechanism for detecting theposition of an operators hands during the operation of a power tool, thepower tool comprising: an active portion of the power tool; a handleportion for manipulating the position of said active portion of thepower tool; a base having a guide surface for guiding a workpiece towardengagement with said active portion, said base including a fencestructure extending substantially perpendicularly from said guidesurface; a first sensor disposed on said handle and operable to detectthe presence of an operator's hand on said handle; a second sensordisposed on one of said base and said fence of the power tool, the powertool configured to activate said active portion of the power tool whenthe operator's hands are detected by said first and second sensor. 4.The power tool of claim 3 wherein said first and second sensors areelectrically connected in series.
 5. The power tool of claim 3, furthercomprising a third sensor disposed on the power tool, said third sensorelectrically connected in parallel with said second sensor and saidsecond and third sensor electrically connected in series with said firstsensor.
 6. A sensing mechanism for detecting the position of anoperators hands during the operation of a power tool comprising: anactive portion of the power tool; a guard oriented proximate to saidactive portion of the power tool; a light emitting device disposed on afirst portion of said guard and operable to emit light; a lightreceiving device disposed on a second portion of said guard andconfigured to receive light emitted from said light emitting device; anda controller electrically connected to said light receiving device andoperable to initiate a protective operation when an object interruptsthe light being received by said light receiving device.
 7. A method ofalerting a user in close proximity to an active portion of a power tool,comprising: providing an electrostatic charge generator disposedproximate to the active portion of the power tool; generating anelectrostatic charge on the active portion of the power tool; andtransferring a charge from the active portion of the power tool to theuser, the user being in close proximity to the active portion therebyalerting the user of its close proximity to the active portion of thepower tool.
 8. A method for detecting the presence of an operator'sextremity during the operation of a power tool comprising: providing atransmitter disposed proximate to an active portion of the power tool;providing a receiver disposed proximate to said transmitter;transmitting a signal from said transmitter toward a workpiece being fedinto said active portion of the power tool; receiving said signal bysaid receiver; determining depth of said workpiece based on said signalreceived by said receiver; and activating a protective operation upondetecting a change in the depth of the workpiece.
 9. The method of claim8 wherein said transmitter is an ultrasound sensor.
 10. The method ofclaim 8 wherein said transmitter is a depth sensor.
 11. A method fordetecting the presence of an operator's extremity during the operationof a power tool, comprising: providing a light emitting device disposedproximate to an active portion of the power tool; providing a lightreceiving device disposed proximate to the active portion of the powertool and configured to receive light emitted from said light emittingdevice; transmitting light from said light emitting device to said lightreceiving device; determining thickness of a workpiece being translatedbetween said light emitting device and said light receiving device,where the measured thickness of the workpiece is based on the amount oflight received by said light receiving device; and activating aprotective operation upon detecting a change in the thickness of theworkpiece. 12 The method of claim 11 wherein the step of determining thethickness of said workpiece includes comparing a change in an amount oflight received by said light receiving device.
 13. A method fordetecting the presence of an operator's extremity during the operationof a power tool comprising: transmitting an electrical signal from atransmitter through a plurality of signal sending emitters disposedadjacent to an active portion of the power tool; receiving saidelectrical signal at a receiver adjacent to said active portion defininga measured value; comparing said measured value to a predeterminedthreshold; and activating a protective operation if said measured valuefalls outside said predetermined threshold.
 14. A safety mechanism forprotecting a user from an active portion of a power tool, comprising: aguard disposed proximate to the active portion of the power tool, theguard providing a barrier between the active portion of the power tooland the user, said guard operable to translate between a first positionand a second position, said first position leaving a portion of theactive portion of the power tool exposed, said second position leaving asmaller amount of said portion of the active portion of the power toolexposed; an engagement member disposed on said guard and operable toengage the active portion of the power tool; and a trigger deviceoperable to deploy said engagement member into engagement with theactive portion of the power tool, thereby rapidly translating said guardfrom said first position to said second position.
 15. A safety mechanismfor alerting a user of a nearby active portion of a power tool,comprising: a plurality of flexible longitudinal members radiallydisposed around the active portion of the power tool, said wire elementsoperable to concurrently rotate with the active portion of the powertool during operation thereof, said wire elements extending a distancebeyond an outermost edge of the active portion of the power tool,thereby contacting an extremity of the user and alerting the user priorto the user contacting the active portion of the power tool.
 16. Thesafety mechanism of claim 15 wherein the power tool is further definedas a miter saw such that the plurality of flexible longitudinal membersare coupled to an arbor of said miter saw.
 17. A safety mechanism forprotecting an extremity of a user from an active portion of a powertool, comprising: a first gear fixed for rotatable movement with theactive portion of the power tool; a second gear selectively fixed forrotation with said first gear; a longitudinal member disposed on saidsecond gear for rotation therewith, said longitudinal member extending adistance beyond an outermost edge of the active portion of the powertool, said longitudinal member operable to translate adjacent to theactive portion of the power tool; and an actuation member for deployingsaid second gear into an intermeshed relationship with said first gear,said longitudinal member thereby rotating adjacent to the active portionof the power tool to urge the user's extremity away from the activeportion of the power tool.
 18. A safety mechanism for protecting anextremity of a user from an active portion of a power tool, comprising:a rigid plate member having a planar work surface, the active portionextending through a passage formed in said rigid plate member in a firstposition, said plate member movable from said first position to a secondposition whereby said plate member extends at a position beyond an outercircumference of the active portion of the power tool; and an actuationmechanism operable to deploy said rigid plate member from said firstposition to said second position thereby urging a nearby user extremityaway from the active portion of the power tool.
 19. A safety mechanismfor protecting an extremity of a user from an active portion of a powertool, comprising: a table portion of the power tool; a support armpivotally coupling said table portion of the power tool to the activeportion of the power tool; a longitudinal member disposed proximate tothe active portion of the power tool, said longitudinal member operableto translate from a first position away from the table portion of thepower tool to a position slidably engaging said table portion; and anactuation mechanism for deploying said longitudinal member from saidfirst position to said second position, thereby pivoting said supportarm and active portion of the power tool away from said table portion ofthe power tool.
 20. A safety mechanism for protecting an extremity of auser from an active portion of a power tool comprising: an inflatablevessel disposed proximate to the active portion of the power tool; andan inflation device for rapidly inflating said inflatable vessel,thereby expanding said inflatable vessel in a direction toward the userextremity and thus urging the user extremity away from the activeportion of the power tool.
 21. A safety mechanism for protecting a userfrom an active portion of a power tool, comprising: a guard disposedproximate to the active portion of the power tool, the guard providing abarrier between the active portion of the power tool and the user, saidguard operable to translate between a first position and a secondposition, said first position leaving a portion of the active portion ofthe power tool exposed, said second position leaving a smaller amount ofsaid portion of the active portion of the power tool exposed; and adeployment mechanism disposed on a frame of the power tool adjacent saidguard, said deployment mechanism operable to translate said guard fromsaid first position to said second position.
 22. The safety mechanism ofclaim 21 wherein said deployment mechanism further comprises anelectrically actuated charge.
 23. The safety mechanism of claim 21wherein said deployment mechanism further comprises an explosive device.24. A safety mechanism for protecting an extremity of a user from anactive portion of a power tool, comprising: an electromagnet disposed ona portion of the power tool adjacent the active portion thereof; aprojectile magnet magnetically coupled to said electromagnet andconfigured to project towards an area of the power tool at which aworkpiece intersects with the active portion of the power tool; and acontroller electrically connected to the electromagnet and operable todeploy the projectile magnet from the electromagnet, thereby deflectingthe extremity of the user from the active portion of the power tool. 25.The safety mechanism of claim 24 wherein the controller is operable tochange the polarity of said electromagnet, thereby causing deployment ofsaid electromagnet.
 26. The safety mechanism of claim 24, furthercomprising a sensing mechanism disposed proximate to the active portionof the power tool and operable to detect a dangerous condition relativeto the operation of the power tool, said controller being operable todeploy said projectile magnet upon detection of a dangerous condition bysaid sensing mechanism.
 27. A safety mechanism for stopping a saw bladeof a power tool, comprising: a frame member interconnected to the activeportion of the power tool, said frame member including a brake memberextending therefrom in a first position adjacent to the active portion;a biasing member coupled on a first end to said frame member adjacentsaid brake member and on a second end to an arbor of the power tool,said biasing member biasing said brake member to said first position;and a gearing member engaged to said frame member, said gearing membermovable to translate said brake member through said frame member fromsaid first position to a second position whereby said brake memberengages the active portion of the power tool thereby bringing the activeportion of the power tool to a complete stop.
 28. A safety mechanism forprotecting a user from an active portion of a power tool, comprising: aframe member extending proximate to the active portion of the powertool; a strap including a first end releasably coupled to a retainingmember and a second end disposed on said frame member, said retainingmember movable from a first position whereby said strap is coupledthereto and a second position whereby said strap is uncoupled therefrom;a biasing member disposed adjacent to said strap, said biasing memberbiasing said strap into said active portion of the power tool when saidretaining member is in said second position; and a friction devicecooperating with said strap for slowing the active portion of the powertool as said strap engages said active portion of the power tool.
 29. Asafety mechanism for protecting a user from an active portion of a powertool, comprising: a frame member extending proximate to the activeportion of the power tool; an arm rotatably coupled to said frame memberon a first end and coupled to the active portion of the power tool on anopposite end; and a strap including a first end coupled to a retainingmember and a second end disposed on said frame member, said retainingmember movable between a first position and a second position, saidretaining member located adjacent to the active portion of the powertool in said first position, said retaining member engaged to the activeportion of the power tool in said second position, said arm configuredto rotate upward upon engagement of said retaining member with theactive portion of the power tool thereby moving said active portion ofthe power tool away from the user.
 30. A safety mechanism for protectinga user from an active portion of a power tool, comprising: a framemember extending proximate to the active portion of the power tool; astrap coupled to a shuttle on a first end and disposed on said framemember on an opposite end; a first biasing member for biasing saidshuttle toward the active portion of the power tool; and a releasemechanism for deploying said shuttle from a first position whereby saidshuttle is retained by said release mechanism to a second positionwhereby said release mechanism releases said shuttle toward the activeportion of the power tool, said shuttle operable to grasp the activeportion of the power tool and thereby translate the active portion ofthe power tool away from the user about a pivot point disposed on saidframe member.
 31. The safety mechanism of claim 30 wherein said releasemechanism includes a pin member retained in said shuttle by a fuse, saidpin member including a second biasing member urging said pin away fromengagement with said shuttle, said fuse operable to release said pinthereby allowing said second biasing member to urge said pin away fromsaid shuttle.
 32. A safety mechanism for protecting a user from anactive portion of a power tool, comprising: a work surface extending ona substantially perpendicular plane relative to the active portion ofthe power tool, the active portion extending through a passage disposedon said work surface and defining an operable position; and an actuationmechanism connected to the active portion of the power tool and operableto deploy said active portion of the power tool from said operableposition to a retracted position where the active portion is below theplane of the work surface.
 33. A safety mechanism for protecting a userfrom an active portion of a power tool, comprising: an arm coupled tothe active portion of the power tool at a first end and coupled to aframe of the power tool by way of a pivot joint at a second end; and apawl disposed on said frame adjacent to the active portion of the powertool, said pawl operable to displace into engagement with the activeportion of the power tool thereby urging the active portion of the powertool to rotate with said arm about said pivot joint and away from theuser.
 34. The safety mechanism of claim 33 wherein said frame furtherincludes a link arm extending substantially parallel from and coupled tosaid arm, said pawl rotatably coupled to said link arm.
 35. The safetymechanism of claim 33 wherein the active portion of the power tool isdriven upward upon engagement of said pawl with the active portion ofthe power tool.
 36. A safety mechanism for protecting a user from anactive portion of a power tool comprising: an arm coupled to the activeportion of the power tool at a first end and coupled to a frame of thepower tool by way of a pivot joint at a second end; and an actuationmechanism disposed on said frame adjacent to said arm and operable toactuate said arm and thus the active portion of the power tool aboutsaid pivot joint away from the user.
 37. The safety mechanism of claim36 wherein said actuation mechanism includes an explosive device. 38.The safety mechanism of claim 36 wherein said actuation mechanismincludes a mechanical spring.
 39. A safety pawl for engaging an activeportion of a power tool, comprising: a main body portion having a firstportion coupled for pivotal rotation about a frame of the power tool,said main body portion further including a first surface including aninterlocking feature arranged thereon; an engaging portion disposed on asecond portion of said main body portion, said engaging portionincluding a second mating surface having a plurality of complementarygrooves incorporated thereon, said second mating surface mating withsaid main body portion at said interlocking feature; and a biasingmember coupled to said frame of the power tool on a first end andinterconnected to the pawl on an opposite end, said biasing memberoperable to bias the pawl into engagement with the active portion of thepower tool.
 40. The safety pawl of claim 39 wherein said interlockingfeature includes a series of grooves formed on said first surface. 41.The safety pawl of claim 39 wherein said main body portion is comprisedof polymeric material.
 42. The safety pawl of claim 39 wherein saidengaging portion is comprised of elastomeric material.
 43. A method forengaging an active portion of a power tool with a two piece safety pawl,the method comprising: sensing a user extremity in close proximity tothe active portion of the power tool; rotating the safety pawl about aframe of the power tool into contact with the active portion of thepower tool, the safety pawl having a removable engagement portion forengaging the active portion of the power tool; removing the engagementportion of the safety pawl; and inserting a new engagement portion ontothe safety pawl.
 44. The method of claim 43 wherein the step of removingthe engagement portion includes the step of withdrawing the engagementportion from the active portion of the power tool.
 45. A releasemechanism for releasing an engaging member into an active portion of apower tool, said release mechanism comprising: a biasing member having afirst end and a second end, said first end coupled to a portion of thepower tool and said second end coupled to the engaging member, saidbiasing member biasing the engaging member toward the active portion ofthe power tool; a first magnet disposed on a portion of the engagingmember; a second magnet disposed on a portion of the power tool, saidsecond magnet normally attracted to said first magnet with sufficientforce to overcome the bias of said biasing member and maintain theengaging member in a position away from the active portion of the powertool; and a coil disposed around one of said first and second magnetsfor controlling the polarity thereof, said coil operable to change thepolarity of said one of said first and second magnets thereby allowingsaid biasing member to urge the engaging member toward the activeportion of the power tool.
 46. A release mechanism for releasing anengaging member into an active portion of a power tool, said releasemechanism comprising: a biasing member coupled to a portion of the powertool on a first end and coupled to the engaging member on a second end,said biasing member biasing the engaging member toward the activeportion of the power tool; a fuse element selectively coupling theengaging member to a portion of the power tool away from the activeportion of the power tool; and a controller for uncoupling said fuseelement thereby allowing said biasing member to urge the engaging membertoward the active portion of the power tool.
 47. The release mechanismof claim 46 wherein said fuse element includes an electricallyconductive wire having first and second ends coupled together, said wirearranged in a loop.
 48. The release mechanism of claim 46 wherein saidcontroller applies a current to said wire thereby causing said wire tofail.
 49. A safety mechanism for releasing an engaging member into anactive portion of a power tool, said safety mechanism comprising: abiasing member coupled to a portion of the power tool on a first end andcoupled to the engaging member on a second end, said biasing memberbiasing the engaging member toward the active portion of the power tool;a latch selectively coupled to a portion of the engaging member; and asolenoid for inducing a magnetic field thereby magnetically couplingsaid latch thereto in a restrained position and for selectively reducingsaid magnetic field in a release position, said latch actuating out ofengagement with said portion of the engaging member in said releaseposition thereby allowing said biasing member to bias the engagingmember toward the active portion of the power tool.
 50. A safetymechanism for protecting an extremity of a user from an active portionof a power tool, comprising: a housing; a deployment carrier disposed insaid housing for actuating toward the active portion of the power tool;a strap element for selectively engaging the active portion of the powertool, said strap element coupled to said deployment carrier on a firstend and coupled to a storage element on an opposite end, said storageelement operable to store an intermediate portion of said strap elementin a first position and rapidly release said intermediate portion ofsaid strap element in a second position, said deployment carriercoupling said first end of said strap element to the active portion ofthe power tool in said second position; a friction device forcooperating with one of said strap element and said storage element torapidly slow the active portion of the power tool upon coupling of saidstrap element to the active portion of the power tool; and a deploymentmechanism for deploying said deployment carrier toward the activeportion of the power tool.
 51. The safety mechanism of claim 50 whereinsaid strap element includes light-weight fiber material.
 52. The safetymechanism of claim 50 wherein said friction device includes a drumrotating adjacent a disk member, said drum including said strap elementcoiled therearound, one of said drum and disk member including afriction material disposed thereon, said friction material resistingrotation of said drum and thereby deployment of said strap element uponcoupling of said strap element to the active portion of the power tool.53. The safety mechanism of claim 50 wherein said strap element issecured in channels arranged on said deployment carrier.
 54. A safetymechanism for protecting an extremity of a user from an active portionof a power tool, comprising: a support arm pivotally coupling a frame ofthe power tool to the active portion of the power tool; a strap elementdisposed in a first position proximate to the active portion of thepower tool; a deployment module disposed on the power tool, saiddeployment module cooperating with said strap element to displace saidstrap element from said first position to a second position whereby anengaging portion of said strap element engages the active portion of thepower tool; and a friction element for slowing the deployment of saidstrap element upon engagement of said engaging portion of said strapelement to the active portion of the power tool.
 55. A safety mechanismfor protecting an extremity of a user from an active portion of a powertool, comprising: a frame of the power tool including a working surfacefor sliding a workpiece therealong into engagement with the activeportion of the power tool; a support arm having a first end coupled to aframe of the power tool at a pivot joint and a second end coupled to theactive portion of the power tool; and a selectively expandable elementcoupled to said frame of the power tool at a first end and coupled tosaid support arm on an opposite end, said expandable element operable todisplace said support arm about said pivot joint from a first positionwhereby the active portion of the power tool is proximate to saidworking surface to a second position whereby said support arm and thussaid active portion of the power tool are displaced away from saidworking surface.
 56. A safety mechanism for protecting an extremity of auser from an active portion of a power tool comprising: a support armpivotally coupling a frame of the power tool to the active portion ofthe power tool; a first gear disposed on said support arm and fixed forrotation therewith; a second gear disposed on one of said frame andsupport arm, said second gear operable to engage said first gear androtate said first gear thereby pivoting the support arm and activeportion upward and away from contact with the user; and a sensingmechanism disposed proximate to the active portion of the power tool andoperable to detect a dangerous condition relative to the operation ofthe power tool, the sensing mechanism being operable to deploy saidsecond gear into an intermeshed relationship with said first gear.
 57. Asafety mechanism for protecting an extremity of a user from an activeportion of a power tool, comprising: a frame of the power tool includinga support structure for coupling the active portion of the power toolthereto; a firing device disposed proximate to the active portion of thepower tool for deploying a projectile into engagement with the activeportion of the power tool, said projectile operable to preclude furtherrotation of the active portion of the power tool upon engagementtherewith; and a sensing mechanism disposed proximate to the activeportion of the power tool and operable to detect a dangerous conditionrelative to the operation of the power tool, the sensing mechanism beingoperable to trigger said firing device.
 58. The safety mechanism ofclaim 57 wherein said firing device is coupled to a guard of the powertool, the guard partially covering a portion of the active portion ofthe power tool.
 59. The safety mechanism of claim 57 wherein said firingdevice includes an explosive device.
 60. A safety mechanism forprecluding further movement of an active portion of a power tool,comprising: a saw blade including a plurality of apertures radiallydisplaced therearound; a rod movable from a first position whereby saidrod is maintained in a static position proximate to said saw blade to asecond position whereby said rod is actuated through one of saidplurality of apertures, said rod operable in said second position toresist movement of said saw blade; a biasing member for selectivelyurging said rod into said second position; and a sensing mechanismdisposed proximate to the active portion of the power tool and operableto detect a dangerous condition relative to the operation of the powertool, the sensing mechanism being operable to release said rod from saidfirst position thereby allowing said biasing member to urge said rodinto said second position.
 61. A safety mechanism for precludingrotation of an active portion of a power tool, the safety mechanismcomprising: a saw blade; at least one cam member disposed in a firstposition proximate to said saw blade; a retaining member retaining saidat least one cam member in said first position; a biasing member forbiasing said at least one cam member toward said saw blade; and arelease mechanism cooperating with said at least one cam member forurging said at least one cam member from said first position to a secondposition whereby said at least one cam member engages said blade tobring said saw blade to a complete stop.
 62. The release mechanism ofclaim 61 wherein said release mechanism includes a fuse memberinterconnected between an electric module and a spacer, said electricmodule operable to send a high current charge onto said fuse therebyfailing said fuse and releasing said retaining member allowing said atleast one cam to actuate toward said saw blade.
 63. A safety mechanismfor selectively inhibiting rotation of an active portion of a powertool, comprising: a first gear fixed for rotation with the activeportion of the power tool; a second gear drivingly connected to saidfirst gear; and a deployment element selectively movable from a firstposition whereby said deployment element is statically arrangedproximate to said first and second gear to a second position wherebysaid deployment element is displaced into engagement with at least oneof said first and second gear thereby precluding rotation of said atleast one of said first and second gear and thus the active portion ofthe power tool.
 64. The safety mechanism of claim 63 wherein saiddeployment is biased toward said second position.
 65. A protectionmechanism for protecting a drive system of a power tool upon a rapidstop event of an active portion of said power tool, comprising: aspindle for mounting a saw blade therearound, said spindle rotating in afirst operating mode concurrently with said saw blade and rotatingindependently from said saw blade in a second operating mode; and a sawclamp selectively coupled to a saw blade, said saw clamp including abreakaway portion for selectively coupling said saw clamp to saidspindle, said breakaway portion operable to maintain said saw clamp insaid first operating mode and operable to disengage said saw clamp fromsaid spindle thereby allowing said spindle to rotate in said secondoperating mode.
 66. A safety mechanism for precluding rotation of anactive portion of a power tool, comprising: a saw blade rotatablycoupled to the power tool; a cam member disposed adjacent to said sawblade, said cam member movable from a first position whereby said cammember is restrained away from said saw blade to a second positionwhereby said cam member is actuated into said saw blade, said cam memberoperable to preclude rotation of said saw blade upon engagement withsaid saw blade; a latch for selectively releasing said cam member fromsaid first position to said second position; and a biasing member forbiasing said cam member into said saw blade.
 67. A safety mechanism forprotecting an extremity of a user from an active portion of a powertool, comprising: a saw blade fixed for rotation on the power tool; anda plurality of guard members radially mounted around said saw blade,said guard members movable from a first position whereby said guardmembers extend to a position within an outer edge of said saw blade to aposition whereby said guard members extend to a position beyond saidouter edge of said saw blade.
 68. A safety system for retracting a sawblade of a table saw under the table portion of the table saw to preventcontact between the operator and the saw blade, comprising: an arborbracket supporting the rotating saw blade of the table saw and coupledto a portion of the table saw for positioning the rotating saw bladerelative to the table portion of the table saw; a sector gear adapted totranslate along a portion of said arbor bracket, said sector gearincluding a gearing portion; a clutch mechanism releasably coupling saidarbor bracket to said sector gear; a selection mechanism engaging thegearing portion of said sector gear and operable to control the positionof said sector gear; and an actuating device coupled to said arborbracket and said sector gear, said actuating device operable totranslate said arbor bracket relative to said sector gear to preventcontact between the saw blade and the operator.
 69. A method fordetecting operator contact with an active portion of a woodworkingmachine, comprising: transmitting an electrical signal from atransmitter to a receiver, said transmitter being electrically coupledto the active portion of the power tool which is in turn electricallycoupled to said receiver; detecting said electrical signal at saidreceiver; deriving a threshold value indicative of operator contact withthe active portion of the power tool; adjusting said threshold valuebased on an electrical load associated with the operation of the activeportion of the power tool; and activating a protective operation inrelation to the active portion of the power tool when said electricalsignal exceeds said threshold value.
 70. The method according to claim69, further comprising the steps of comparing said electrical signaldetected at said receiver to a reference value and adjusting saidelectrical signal from said transmitter based on the comparison of saidelectrical signal detected at said receiver to said reference value. 71.A contact detection system for a power tool having an active portion;comprising: a transmitter capacitively coupled to the active portion ofthe power tool and operable to transmit an electrical signal to theactive portion of the power tool; a receiver capacitively coupled to theactive portion of the power tool and operable to receive said electricalsignal transmitted to the active portion of the power tool; and adetection circuit electrically connected to said receiver, saiddetection circuit operable to derive a threshold value indicative ofoperator contact with the active portion of the power tool and toactivate a protective operation in relation to the active portion of thepower tool when said electrical signal exceeds said threshold value,where said detection circuit adjusts said threshold value based on anelectrical load associated with the operation of the active portion ofthe power tool.
 72. A contact detection system for a power tool havingan active portion; comprising: a transmitter capacitively coupled to theactive portion of the power tool and operable to transmit an electricalsignal to the active portion of the power tool; a receiver capacitivelycoupled to the active portion of the power tool and operable to receivesaid electrical signal transmitted to the active portion of the powertool; and a controller connected to said receiver, said controlleroperable to detect a variation in said electrical signal and to activatea protective operation in relation to the active portion of the powertool when said variation in said electrical signal exceeds saidthreshold value, where said detection circuit adjusts said thresholdvalue based on an electrical load associated with the operation of theactive portion of the power tool.
 73. A braking system for stopping arotating circular saw blade of a power tool rapidly, the systemcomprising: a rigid base member; an arm having a first and a second end,the first end of the arm rotatably coupled to the rigid base member, thesecond end of the arm coupled to the rotating circular saw blade; abrake device coupled to the arm, the brake device operable to engage thecircular saw blade to stop rotation of the circular saw blade; and anactivation device coupled to the brake device and the rigid base member,the activation device including an explosive charge operable to compelthe brake device into engagement with the circular saw blade upon theoccurrence of a predetermined event.
 74. A safety mechanism forprecluding rotation of an active portion of a power tool, comprising: asaw blade rotatably coupled to the power tool; a cam member disposedadjacent to and fixed for rotation with said saw blade; a link armselectively movable from a first position adjacent said cam member to asecond position in communication with said cam member; and a brakecoupled to said link arm, said brake movable from a position adjacentsaid saw blade to a position engaging with said saw blade upon movementof said link arm to said second position.
 75. A mounting arrangement ofa power tool for selectively aligning a brake into proper orientationwith one of a plurality of saw blades having different diameters: a sawblade coupled to the power tool; an arbor bracket for rotatably couplingsaid saw blade to the power tool, said arbor bracket extending laterallyfrom said saw blade and including a slot formed on an outer portionthereof; and a brake selectively slidably interconnected to said arborbracket at said slot, said brake movable along said slot for positioningsaid brake at varying degrees of proximity relative to said saw bladefor accommodating a saw blade of the one of a plurality of saw bladeshaving a distinct diameter from the other of said plurality of sawblades.